The Republican field for president is expected to grow by three this week, with former Vice President Mike Pence, ex-New Jersey Gov. Chris Christie and North Dakota Gov. Doug Burgum joining the race.

Meanwhile, another Republican — New Hampshire Gov. Chris Sununu — announced he won’t run for the White House.

Pence filed paperwork Monday with the Federal Election Commission to formally launch his bid. He will announce his candidacy Wednesday at a rally in Des Moines, Iowa, followed by a CNN town hall that night.

Pence’s entry into the race sets the stage for a showdown between him and his ex-boss, former President Donald Trump. Their relationship soured when Pence refused Trump’s pleas to reject the certification of President Joe Biden’s victory in 2020.

At Sen. Joni Ernst “Roast and Ride” event Saturday in Des Moines, where eight candidates -- or soon-to-be candidates -- gathered, Pence, 63, demonstrated the challenging balancing act he faces — touting the accomplishments of the Trump administration he served in while selling himself as a better alternative to the former president. 

“We gave America a new beginning for life, and we can do it all again,” Pence said. 

Christie, 60, will announce he’s running at a town hall-style meeting Tuesday evening at Saint Anselm College in Goffstown, New Hampshire.

The former New Jersey governor, who also ran for president in 2016, has been a longtime Trump ally but broke with the former president over his refusal to accept the results of the 2020 election.

Now one of Trump’s loudest Republican critics, Christie has signaled he plans to aggressively attack Trump on the campaign trail. Christie has said candidates who “hope that he [Trump] implodes and that, if they are nice to him, that they’ll inherit his voters” are making a mistake.

“You can't beat Donald Trump by playing bumper pool and hitting it off three cushions and hope it goes in the hole,” Christie told ABC News’ “This Week” last month. “That's not the way it works.”

Burgum, 66, will reportedly announce his candidacy Wednesday in Fargo, North Dakota.

A tech magnate now serving his second term as governor, Burgum lacks name recognition compared to most of the other candidates. 

Burgum posted a campaign-style video on social media Tuesday ahead of what he called a “big announcement,” but he has stopped short so far of saying publicly he’s running for president. 

“We need new leadership for our changing economy,” he said in the 3½-minute video. 

Sununu, who is serving his fourth two-year term as New Hampshire’s governor, announced Monday he’s not running for president in an interview with CNN and an op-ed in The Washington Post. 

“The stakes are too high for a crowded field to hand the nomination to a candidate who earns just 35 percent of the vote, and I will help ensure this does not happen,” he wrote in The Post. 

Republicans who previously announced they’re running are Trump, Florida Gov. Ron DeSantis, former Ambassador to the United Nations Nikki Haley, Sen. Tim Scott of South Carolina, former Arkansas Gov. Asa Hutchinson, entrepreneur Vivek Ramaswamy and conservative radio host Larry Elder.

The first GOP debate will be held Aug. 23 in Milwaukee.