The GOP presidential campaigns are fighting to win and maintain the support of nearly 2,500 total delegates who will go to the Republican National Convention. Candidate Donald Trump still needs 393 to clinch the nomination outright. If he comes up short, that would trigger a contested convention, freeing delegates to vote for any candidate.
The art of courting delegates takes many forms and pushes boundaries, reports CBS News correspondent Julianna Goldman. Since the last contested Republican convention was 40 years ago, campaigns and their lawyers are figuring out how far the law can take them.
"You're basically saying, 'Delegate, listen, we're going to send you to Mar-a-Lago on a Boeing 757, you're going to use the spa, you're going to this, you're going to that.' That's a corrupt system. That's not a democracy," Trump said last Sunday while campaigning in Staten Island.
Trump has been lashing out at his rivals, suggesting they're essentially buying delegates' votes.
"It's a rigged system, it's a crooked system. It's a 100 percent crooked," he said.
Campaign finance experts like attorney Kenneth Gross, a former associate general counsel of the Federal Elections Commission, say he has a point.
"I don't think you'll see any brown paper bags with cash in it, but certainly you're going to see some efforts to influence these delegates in some way," Gross said.
Federal law allows delegates to have their convention trips paid for, as long as the money isn't from businesses, labor unions, foreign nationals and federal contractors. Generally, there are no limits on how much delegates can accept, and they do not have to report any of it.
That means flights on private jets, nights in five-star hotels and dinners at gourmet restaurants - paid for by wealthy donors, super PACs, or the campaigns themselves -- is perfectly legal.
"Some of it may be innocent -- you know, 'Let's go out for a drink,' or it could be a lavish weekend somewhere, or it could be a promise for a specific position," Gross described.
At the last contested Republican convention in 1976, Gerald Ford wooed delegates with promises of trips on Air Force One and invites to state dinners. Ronald Reagan countered with calls from his Hollywood pals including Pat Boone, Jimmy Stewart and John Wayne.
But delegates tend to be lifelong political junkies, and in the end, convention veterans think they will be swayed not by the wining and dining but by good old-fashioned horse trading.
"Would you like a job at the national committee? Would you like to be national chairman?" said Rick Davis, Sen. John McCain's campaign manager in the 2008 race. "All these patronage jobs within the party and within campaigns are gonna be part of the conversation."
"But does it raise any corruption questions?" Goldman asked.
"Sure. I mean, it's a narrow band walking, right? You're not supposed to promise a job for a vote," Davis said.
Election lawyers say this really is the "Wild West." There's a patchwork of anti-corruption and bribery laws that apply to votes during elections, but it's unclear if that also covers votes during political conventions.