President Donald Trump could face a secret impeachment vote in the Senate if only three Republicans conditioned the ballot on their accepting the rules governing a trial in the chamber, a longtime GOP adviser argued Tuesday.

"If they didn't have to face backlash from constituents or the media or the president himself, who knows how many Republican senators would vote to remove?" Juleanna Glover posed in an opinion piece for Politico.

Glover has advised several Republicans, including former President George W. Bush and former Vice President Dick Cheney.

Senate Majority Leader Mitch McConnell, R-Ky., has said that he would immediately hold a trial if articles of impeachment were approved by the House.

However, the U.S. Constitution "does not set many parameters for the trial" beyond requiring the chief justice of the Supreme Court to preside and requiring a two-thirds vote of the chamber.

"That means the Senate has sole authority to draft its own rules for the impeachment trial, without judicial or executive branch oversight," Glover said.

And, given the current partisanship on Capitol Hill, "McConnell and his fellow Republicans are much more likely to dictate the rules with little input from Democrats."

Any guidelines must be approved by 51 of the chamber's 53 Republicans.

"That means that if only three Republican senators were to break from the caucus, they could block any rule they didn't like," Glover argued. "Those three senators, in turn, could demand a secret ballot and condition their approval of the rest of the rules on getting one."

Such a ballot ultimately could be good for President Trump, Glover concluded.

He would soon realize that "his best course could be to cut a deal, trading his office for a get-out-of-jail-free card — a clean slate from prosecutors — just as Vice President Spiro Agnew did."