CLEVELAND — The balloons and confetti had not yet dropped on Donald Trump, and already the race to replace him as the 2020 GOP nominee was well underway Thursday.

All week, ambitious Republicans with their eyes focused four years ahead had circulated among delegations from key states, shaking hands, making contacts and subtly touting their qualifications.

But Sen. Ted Cruz's refusal to endorse the top of the ticket during his speech at the convention Wednesday night brought the contest into public view.

Cruz has not formally announced that he will make another run for the White House. But it hardly mattered.

The morning after he was booed off the convention stage by angry Trump supporters, the Texas senator tried to position himself as the top Republican willing to buck Trump and as a conservative torch-bearer determined to put principle before party.

“I wasn't elected to do the convenient thing; I was elected to stand up and do what's right,” Cruz said during a breakfast exchange with delegates from his home state.

With that, the 2020 campaign was all but off and running.

Convention week always provides a venue for future presidential hopefuls to introduce themselves to the party faithful and big-money donors.

In 2004 at the Republican National Convention in New York, then-Massachusetts Gov. Mitt Romney threw a party for delegates from early primary states on the retired aircraft carrier Intrepid.

Eight years later, he was the nominee.

This time, at least a half-dozen Republicans followed a similar plan even as other potential candidates, including Sens. Marco Rubio of Florida and Ben Sasse of Nebraska, stayed away.

Ohio Gov. John Kasich waged what at times resembled a shadow convention with a packed schedule of daily events — none of which were held near the Quicken Loans Arena stage where the official convention took place.

Romney's 2012 running mate, House Speaker Paul Ryan of Wisconsin, had little choice but to share the spotlight with Trump, announcing the roll call vote that handed the businessman the nomination. But Ryan also found time for several other events that showcased his claim to be the candidate of new ideas.

Veteran campaign trail warriors Rick Santorum, Mike Huckabee and Newt Gingrich made the rounds — Gingrich on a boat tour with supporters.

Other up-and-comers, including South Carolina Gov. Nikki Haley, Iowa Sen. Joni Ernst and Arkansas Sen. Tom Cotton, let it be known they were in town.

But nowhere was the next GOP contest more on display than with Cruz.

The first-term senator didn't close the door on an eventual endorsement of Trump, but after their bitter primary campaign, during which Trump attacked his rival's wife and father, Cruz made it clear the GOP nominee had not earned his vote.

“I am watching, and I'm listening,” Cruz said at the Texas delegation breakfast. Pushed by his fellow Texans to use his position to unify the party around Trump, Cruz shot back that the GOP is not a “social club” and must hold true to its values.

“We either stand for shared principles or we're not worth anything,” he shouted.

“You got to get over it!” hollered one Texan. “This is politics!”

“This is not a game!” Cruz shot back. “It's not politics. Right and wrong matter.”

The risks for Cruz are clear.

While his stand sets him apart from a GOP establishment that has reluctantly rallied around Trump, his refusal to endorse threatens to prolong the party disunity that has been on display.

The Texas delegation split deeply over their once-favorite son.

“He just eroded his base,” said Gina Castenada, a delegate from Houston, who voted for Cruz during the primary, but wants him to back Trump. “The support will not be there in the next election.”

“I'm proud of him,” said Grant Moody, a Marine who served in Iraq and Afghanistan and is a banking executive in San Antonio.

“I'm still waiting, as I think Senator Cruz, and many conservatives are waiting, for Donald Trump to behave in a manner befitting of the office — to tone down his demeanor.”

lisa.mascaro@latimes.com