The 2024 GOP field is shaping up to be a crowded one, with Mike Pence reportedly poised to face off against his former boss, Donald Trump, plus Ron DeSantis, Nikki Haley and several others.

With Trump viewed as the frontrunner, could anyone bump him out of the picture as the Republican nominee?

David Gergen, presidential advisor to Richard Nixon, Gerald Ford, Ronald Reagan and Bill Clinton, offered his best advice and predictions on Greater Boston.

Gergen said it will be very difficult for candidates to peel votes away from Trump, lest he end up in jail over pending criminal charges against him. He predicted Trump will be the nominee.

He said Trump challengers should stand up for government institutions instead of cultural issues.

"It may not make you more electable in the beginning, but it will give you the better legacy over time, and sometimes if you perservere, you can make it," Gergen said.

"What we want is a president who is effective in carrying out the Constitution, not someone who is effective in squashing it," he added.

Gergen said a candidate like DeSantis could be strong, however his views on issues such as abortion could disqualify him in the eyes of many voters. He said DeSantis and other candidates need to stop "out-Trumping Trump" but pushing themselves further right of the former president.

Watch: The 2024 GOP field will be crowded. Can anyone bump Trump from the nomination?