Waiting until the late August convention in Tampa to select a GOP presidential nominee would essentially hand a second term to President Barack Obama, prominent Senate Republicans said Tuesday.

Some in the GOP are speculating that the four remaining presidential candidates will be unable to secure the required 1,144 delegates, pushing the decision to a convention floor vote that is typically an orchestrated formality. Senate Republicans expect their party to crown a nominee by the time the primary season ends in June, thus avoiding such a scenario. But they caution that failure to do so would be a political disaster.

“It would be a big mistake on our part,” said Sen. Lindsey Graham (R-S.C.), who is not aligned with a presidential candidate. “If we don’t have a nominee [until] Labor Day, we’re in trouble.”

On primary day in Alabama, Hawaii and Mississippi, former Massachusetts Gov. Mitt Romney maintained a sizable delegate lead over former Speaker Newt Gingrich (Ga.), ex-Sen. Rick Santorum (Pa.) and Rep. Ron Paul (Texas). Before Tuesday’s contests, Romney’s count stood at 454, with Santorum in second at 217, followed by Gingrich at 107 and Paul at 47, according to the Associated Press.

Sen. Roy Blunt (R-Mo.), the leader of Romney’s Capitol Hill Whip team, said  that how the governor finished in Alabama and Mississippi could have a major effect on the race going forward.

Blunt suggested that a victory in just one of these conservative Southern states could help Romney wrap up the race sooner rather than later. Given the proportional awarding of delegates in many states and Romney’s occasional trouble securing the votes of self-described “very conservative” voters, even many political observers who expect the governor to win the nomination say it could take him until June.

“I think the way he finishes in these two states today is important,” Blunt said. “I expect to have a nominee by the time we go to the convention.”

Most Congressional Republicans who have made endorsements are backing Romney. But much of their worry over a contested convention, or one that is brokered and produces a different candidate altogether, is born of logistics and timing.

Sen. John McCain (Ariz.), the GOP White House nominee four years ago, said that every day the 2012 primary continues is one less day before Nov. 6 that Republicans can train their campaign fire on Obama’s record and soften the president’s re-election prospects. To underscore his point, McCain cited polling that has at times shown the Republican candidates with low personal favorability numbers and Obama in decent shape for re-election.

“Every day that goes by is a day that’s lost,” said McCain, a Romney supporter.

McCain conceded he wasn’t sure how a contested convention would affect the GOP’s White House prospects. But Sen. John Thune (R-S.D.), also a Romney supporter, said it could be fatal.

Thune said failing to select a nominee by the end of June — any nominee — would allow Obama to escape the damage an opposition GOP campaign might inflict until September, by which time it would be too late to fund and organize an effective national organization capable of competing with the president’s political machine.

In the event of a contested convention, Thune indicated that he would expect the GOP candidates to spend July and August continuing to raise primary campaign money to fund attacks against each other in an effort to sway convention delegates, who are not scheduled to meet in Tampa until Aug. 27.

“That’s incredibly problematic for us. If we’re out there sort of in this uncertainty zone between now and the end of August and we have to turn around in a short time period, put together an organization and resource it, it’s incredibly problematic,” said Thune, the Republican Conference chairman. “I just don’t see it.”

Sen. Jim DeMint (R-S.C.) acknowledged that failing to elect a nominee by the time of the last primary in June — in Utah — could put the Republicans at a disadvantage against Obama. But DeMint, who expects the GOP to at least have a “nominee apparent” by the end of the primary season, said a contested convention might have some positive side effects.

In particular, DeMint said, the intense media focus on the undecided Republican contest would give the GOP candidates a cost-free platform to push ideas and hammer Obama, possibly obscuring coverage of the president.

“I always look for the silver lining; it would keep all eyes on Republicans until the convention,” DeMint said, although he cautioned: “The reality is the raising of money, in that short of time, to come anywhere near what Obama’s going to have, is going to be difficult. We’re going to have to count on the American people to sort it out.”