AMNA NAWAZ: Today was one of the busiest days of the Republican presidential campaign so far, as Mike Pence and Doug Burgum joined the race.

We will look at both of the new candidates, starting with the former vice president.

As Laura Barron-Lopez reports, during his kickoff in Iowa, Pence drew a sharp contrast with his former running mate.

MIKE PENCE (R), Presidential Candidate: I stand before you today as a candidate for president to say to the Republican Party, the Republican Party must be the party of the Constitution of the United States.

(CHEERING AND APPLAUSE) LAURA BARRON-LOPEZ: The right-wing radio host turned politician serving six terms in Congress and four years as Indiana governor before joining the Trump White House now hopes to take the top job himself.

MIKE PENCE: Anyone who puts themselves over the Constitution should never be president of the United States.

(APPLAUSE) MIKE PENCE: And anyone who asks someone else to put them over the Constitution should never be president of the United States again.

(CHEERING AND APPLAUSE) MAN: If you would bow your head and your hearts.

LAURA BARRON-LOPEZ: One of the most outwardly evangelical Christians in government, Pence's faith and conservatism have defined his career.

Elected governor of the Hoosier State in 2012, Pence enacted a staunchly anti-LGBTQ and anti-abortion agenda.

In 2015, Pence supported a bill that allowed businesses to discriminate against LGBTQ customers, under religious objections, a law he quickly amended after facing national backlash.

In the lead-up to his presidential bid, Pence has called for a nationwide abortion ban and an end to the commonly used abortion medication pill mifepristone.

MIKE PENCE: I'd like to see this medication off the market to protect the unborn.

LAURA BARRON-LOPEZ: As Trump's vice president, Pence stood by Trump's side throughout his time in office, until January 6, 2021.

Trump repeatedly pressured Pence to reject certification of the 2020 presidential election and overturn the will of voters.

DONALD TRUMP, Former President of the United States: If Mike Pence does the right thing, we win the election.

LAURA BARRON-LOPEZ: A mob incited by Trump descended on the Capitol, searching for Pence.

RIOTERS: Hang Mike Pence!

Hang Mike Pence!

LAURA BARRON-LOPEZ: Pence refused.

MIKE PENCE: To those who wreaked havoc in our Capitol today, you did not win.

LAURA BARRON-LOPEZ: In the years since, Pence has seesawed between criticizing Trump for his role in the January 6 attacks... MIKE PENCE: When he returned in the months later to the rhetoric he was using before January 6, arguing that I had the right to overturn the election, I just decided it would best that we went our separate ways.

And we have.

LAURA BARRON-LOPEZ: ... but defended him on other matters.

MIKE PENCE: This is nothing short of a -- of a political prosecution being effected by a Manhattan DA who literally campaigned on bringing charges against one particular American.

While potential legal troubles still loom for Trump, including possible obstruction charges for retaining classified documents at Mar-a-Lago, Pence was recently cleared by the Justice Department, which closed its investigation into the discovery of classified documents at his Indiana home.

It's not clear if Pence will break through in a crowded primary, with his former boss leading the pack.

DARYL CHARLSON, Iowa Voter: I think Pence has a really, really great heart.

I think he's very intelligent.

The whole pool is probably one of the best pools I have seen for candidates ever.

I mean, it's just really crazy.

LAURA BARRON-LOPEZ: Pence will join CNN for a prime-time town hall this evening at Grand View University in Des Moines.

He's scheduled to travel to New Hampshire on Friday.

For the "PBS NewsHour," I'm Laura Barron-Lopez.

AMNA NAWAZ: And 400 miles away, in Fargo, North Dakota, Governor Doug Burgum also launched his campaign.

Lisa Desjardins reports on his record.

GOV.

DOUG BURGUM (R-ND), Presidential Candidate: Frankly, big cities can use more ideas and more values from small towns right now.

(CHEERING AND APPLAUSE) LISA DESJARDINS: North Dakota Governor Doug Burgum's presidential pitch is about his roots, far from Washington.

GOV.

DOUG BURGUM: Our whole town was about taking care of each other, about helping those in need, about neighbor helping neighbor.

Every small town in America is like that.

LISA DESJARDINS: In the 1980s, he took a chance, mortgaging his family grain farm to launch Great Plains Software.

That gamble paid off.

He sold the company in the 1990s to Microsoft for $1.1 billion.

MAN: Republican Doug Burgum.

LISA DESJARDINS: In 2016, he tried a new career, entering the governor's race with no political experience.

He easily beat an establishment candidate and won reelection four years later.

Energy policy, including drilling, is a focus for Burgum.

He's accused the Biden administration of waging a war on domestic fossil fuel production.

GOV.

DOUG BURGUM: It is a very simple thing.

If we want to have a global stable world and a strong U.S. economy, then we need to produce energy for ourselves and for our allies.

And we are not doing that.

LISA DESJARDINS: As for his GOP rivals... GOV.

RON DESANTIS (R-FL), Presidential Candidate: Florida is where woke goes to die!

(CHEERING AND APPLAUSE) GOV.

DOUG BURGUM: Woke is what you did at 5:00 a.m. to start the day.

LISA DESJARDINS: ... Burgum is attempting a nuanced contrast on social issues, saying the economy deserves more attention.

But he is socially conservative, recently signing a state law banning abortion at six weeks of pregnancy.

And the Human Rights Campaign says North Dakota is on track to pass more anti-LGBTQ legislation this year than any other state.

That includes a ban on gender-affirming health care for trans youth.

GOV.

DOUG BURGUM: We understand families and parents that are affected by it.

You know, it's a complex emotional issue.

LISA DESJARDINS: On immigration, Burgum recently directed more North Dakota National Guard troops to the Southern border.

But candidate Burgum is now looking east, with plans to talk to voters in Iowa and New Hampshire.

For the "PBS NewsHour," I'm Lisa Desjardins.

AMNA NAWAZ: So, with Burgum and Pence officially in, the Republican field grew by three this week.

Former New Jersey Governor Chris Christie kicked off his campaign last night in New Hampshire, and he's already set himself apart as the most vocal Trump critic in the race.

FMR.

GOV.

CHRIS CHRISTIE (R-NJ), Presidential Candidate: The person I am talking about who is obsessed with the mirror, who never admits a mistake, who never admits a fault, and who always finds someone else and something else to blame for whatever goes wrong, but finds every reason to take credit for anything that goes right, is Donald Trump.

AMNA NAWAZ: With nine candidates now on the stump, we take stock of the race with Whit Ayres.

He is a Republican strategist and the president of North Star Opinion Research.

He's previously consulted Republican candidates, including Senators Marco Rubio and Lindsey Graham and Florida Governor Ron DeSantis.

Whit, good to see you.

thanks for being here.

WHIT AYRES, President, North Star Opinion Research: Good to be here.

Thank you.

AMNA NAWAZ: So when you take a look at this field -- let's take a look at these nine candidates right now who are vying for the Republican nomination -- is this where you expected the Republican field to be right now?

What do you see when you look at this?

WHIT AYRES: We saw that a lot of people were interested and would want to try their hand.

And a lot of people are worried that it's going to be like 2016 all over again, where you divide the non-Trump vote and allowed Trump to win majority -- or a majority of the delegates by getting a plurality of the vote.

But the key is not the number of people who start.

The key is the number of people who stay in long after they could possibly win the nomination.

The model is the Democrats in 2020.

When Joe Biden won South Carolina, within ours, many of the candidates dropped out and endorsed him.

On the other hand, in 2016, candidates like John Kasich stayed in long after he had any realistic chance.

He got 7 percent of the vote in Virginia.

Marco Rubio would have won Virginia and beaten Donald Trump if John Kasich had not been in the race.

So the key to watch for Republicans is how many stay in when they have got no chance.

AMNA NAWAZ: And you say stay in, past those early states, past South Carolina in this case?

WHIT AYRES: Yes, yes, stay in past South Carolina.

Just like the Democrats did with Joe Biden - - after South Carolina, they got out and endorsed him.

AMNA NAWAZ: I want to ask you about some of the specific candidates, especially the ones that joined the race this week.

The line that Mike Pence has to walk here, running against the man alongside whom he served for four years, whose supporters said they wanted to kill him on January 6, what do you make of how he's messaging along those lines right now?

WHIT AYRES: Mike Pence, who, by all accounts, is a very good man, is caught between a rock and a hard place.

He's not Trumpy enough for the Trumpies, and he's too Trumpy for the non-Trumpies.

So he's got a very difficult line to walk.

We will see if he can make that work.

But it's a tough, tough line.

AMNA NAWAZ: What do you make of how Chris Christie has set himself apart now?

Does his ramping up his attacks against Donald Trump, does that force other candidates to meet him where he is?

WHIT AYRES: No.

Chris Christie is very talented and very good at making an argument, very powerful at making an attack on his opponents.

But the Republican Party is split into three factions.

There's a never-Trump faction that's only about 10 percent.

There's an always-Trump faction of about 35 percent.

Those people are always going to be with Trump regardless of the opponent.

The majority of the party, about 55 percent, are maybe-Trump voters.

They have supported him twice.

They would vote for him again against Joe Biden, but they're worried about his electability.

They're worried he carries too much baggage, and they're looking for alternatives.

Chris Christie's message, arguing that Donald Trump is unfit for office, appeals to the never-Trumpers.

But he's going to tap out at about 10 percent.

Saying that Donald Trump was unfit for office is an insult to the maybe-Trump voters who supported him twice.

So he's got no chance with those people.

The other candidates are trying to consolidate the maybe-Trump portion of the party.

AMNA NAWAZ: So I want to play for you one voter we heard from in New Hampshire who speaks exactly to that.

It's a woman named Nancy Malonson.

And here's what she had to say.

NANCY MALONSON, New Hampshire Voter: Trump is amazing, but a lot of people don't like him.

So do we want to be in that situation where they really -- it's just really -- it's sad that our country has so much hatred towards that man.

So maybe we do need new blood.

AMNA NAWAZ: So there are a number of candidates polling in the low single digits right now.

If they want to appeal to people like Nancy Malonson, what's the message that you think those other candidates have to carry forward?

WHIT AYRES: They have to look and act like a successful president of the United States.

They have got to be able to capture public attention.

They have got to be able to capture any kind of excitement that they possibly can.

And who knows.

There's a lot of talent in this field.

And somebody may catch fire, but they're going to have to catch fire in a big way in order to surpass the lead the Donald Trump currently has.

AMNA NAWAZ: In the 40 seconds or so we have left, who do you see among some of those other candidates, Nikki Haley, Tim Scott, Asa Hutchinson, who could break through, particularly in these early states... WHIT AYRES: Yes.

AMNA NAWAZ: ... of Iowa, New Hampshire, Nevada, and South Carolina?

WHIT AYRES: I think any of them could.

The history is replete with candidates who started off as asterisks in the race and then ended up winning Iowa or coming in a close second and then doing really well in New Hampshire.

So it's all a matter of the candidate, kind of campaigns that they run and whether they can catch fire at the right time.

AMNA NAWAZ: You will be tracking it all.

So we will.

Whit Ayres, always good to see you.

Thank you so much.

WHIT AYRES: It's a pleasure.

Thank you.