Donald Trump's GOP Rivals Wrestle With Supporting His Nomination

— -- It’s been a rocky road to Cleveland for Donald Trump’s former GOP rivals.

One by one, the sixteen politicians who made up the most promising Republican presidential field in a generation, bowed out of the race for the White House, bruised and bullied by a brash New York real estate developer with no political experience.

While some endorsed Trump as they exited the race, many actively opposed his insurgent White House bid and campaigned against him until the decisive May primary in Indiana.

But faced with the looming prospect of a Hillary Clinton presidency, most of the former GOP presidential candidates have attempted to reconcile their disagreements with Trump with supporting the Republican nominee for president.

Wisconsin Gov. Scott Walker, who suspended his presidential run after 70 days to help unite Republicans against Trump, announced the Wisconsin delegation’s votes on the floor of the RNC convention Tuesday.

In his convention speech Wednesday, he proclaimed that “Donald Trump is standing with the American people,” and offered his endorsement.

“A vote for anyone other than Donald Trump in November is a vote for Hillary Clinton,” he said – an offering of support Trump wasn’t counting on earlier in the race.

Sen. Marco Rubio, R-Florida, exchanged personal insults with Trump before suspending his campaign, and skipped the convention to remain in Florida, where he’s running for reelection.

Rubio who stands by his primary comments that Trump can’t be trusted with the country’s nuclear codes, recorded a call for party unity that was played in the Quicken Loans Arena.

“After a long and spirited primary, the time for fighting each other is over,” he said, adding that Trump is committed to conservative governance and Supreme Court.

But Sen. Ted Cruz, R-Texas, the only candidate to challenge Trump on the primary map, wasn’t prepared to line up behind the nominee.

On Wednesday, he boldly refused to endorse Trump after congratulating him for winning the nomination.

“If you love your country and you love your children as much as I know that you do, stand and speak, and vote your conscience,” Cruz declared, drawing boos from Trump supporters. “Vote for candidates up and down the ticket who you trust to defend our freedom.”

New Jersey Gov. Chris Christie, who shocked the political world by endorsing Trump soon after ending his own White House bid, could be seen shaking his head with disapproval.

While Cruz embraced Trump early in the GOP primary, their relationship soured after Trump mocked his wife's appearance in a tweet, questioned his eligibility for the presidency, and alleged that Cruz's father was involved in the assassination of President John F. Kennedy. For much of the primary, Trump also referred to Cruz as "Lyin' Ted."

Cruz mentioned Trump’s name just once during his address, while Rubio referenced him twice and Walker did so five times.

ABC News' Adam Kelsey contributed to this report.