Former Vice President Mike Pence has filed the necessary paperwork to launch his presidential campaign, setting himself up for a challenging run against his former boss, Donald J. Trump.

“In 2024, I believe Conservatives have a once-in-a-lifetime opportunity to renew the promise of America!,” Tweeted Saturday, in a thread of campaign-style messages.

“We can be a nation where everyone prospers, and everyone wins. We can have a government that is as good as our people. And we can be a nation where every American is free to live, to work, and to worship, according to the dictates of their faith and conscience!”

Pence, who will turn 64 on Wednesday, submitted the notice to the Federal Election Commission on Monday.

Originally from Columbus, Indiana, Pence shared a video of himself and his wife Karen attending an event over the weekend to support an Iowa Senate candidate. However, he has yet to make an official announcement regarding his candidacy.

Pence, who has consistently polled in the single digits in all public surveys conducted thus far, trails far behind Trump, who has significantly influenced the Republican Party over the past seven years.

He is expected to formally declare his candidacy at a rally in Des Moines on Wednesday, the same day former Governor Chris Christie is anticipated to enter the race, while Governor Doug Burgum of North Dakota is set to announce his bid as well.

Pence is focusing his campaign efforts on Iowa, the first state to hold primaries, where his staunch conservative positions on issues such as abortion could appeal to evangelical voters.

Pence’s advisers view Iowa as a favorable geographical location for the conservative brand he represented before the Trump era. He is banking on the belief that enough remnants of the old Republican Party still exist to garner broad support for his message.

During their time in office together, Pence, whom Trump would often refer to as “out of central casting,” was an unwavering advocate and defender of Trump. This loyalty persisted even as Pence faced a challenging reelection campaign in Indiana during the latter half of the 2016 presidential race.

However, tensions rose between Pence and Trump when the former vice president refused to use his ceremonial role to overturn Joseph R. Biden Jr.’s Electoral College victory on January 6, 2021.

In an earlier interview with CBS News this year, Pence declined to commit to supporting Trump if he were to become the Republican presidential nominee again, stating that “different times call for different leadership.”

Pence has drawn Trump’s ire for his refusal to reject the results of the 2020 presidential election both before and after the Capitol riot on January 6, 2021. In April, he appeared before the grand jury investigating Trump’s attempts to alter the election outcome for more than seven hours.

He enters a crowded field of prominent Republican contenders, including Florida Governor Ron DeSantis, Senator Tim Scott, and former Governor Nikki Haley. Pence is expected to highlight the contrast between himself and Trump and DeSantis. With Trump, he may emphasize Trump’s record on federal spending and programs like Medicare and Social Security.

In March, Pence strongly denounced Trump, stating that the former president’s “reckless words endangered my family and everyone at the Capitol that day.”

Speaking at the Gridiron Club Dinner in Washington, D.C., Pence had restrained criticism for his former boss.

“History will hold Donald Trump accountable,” Pence told the audience.

During his vice presidency, Pence led the White House Coronavirus Task Force in combating the COVID-19 pandemic, chaired the National Space Council, and consistently defended the administration’s agenda while navigating Trump’s cavalier style.