The 3 presidential candidates throwing a wrench in Mitch McConnell's plans

When Sen. Rand Paul (R) of Kentucky brought floor action on the Patriot Act to a standstill early last Saturday, he underscored the challenge that Senate majority leader Mitch McConnell has with his three ideological freshman senators seeking the presidency.

The other two senators are Ted Cruz (R) of Texas and Marco Rubio (R) of Florida. As presidential aspirants, they have broken with GOP tradition and are not patiently “waiting their turn” for a shot at the Oval Office. According to longtime congressional observers, such lawmakers have no Senate tradition or deep love of the institution.

Senator Paul’s campaign slogan, for one, is “defeat the Washington machine.”

“There’s a new breed in the Senate, and we have seen the manifestations of it,” Sen. John McCain (R) of Arizona said after the Senate showdown, according to The Washington Post.

“It’s a totally different era,” says Jim Manley, who was the spokesman for former majority leader Harry Reid (D) of Nevada in 2008, when four Democratic senators – Joe Biden, Hillary Clinton, Christopher Dodd, and Barack Obama – were running for the presidency. What’s unusual this time is that these three Republicans “care very little, if anything, about the Senate and its customs and traditions,” says Mr. Manley.

A total of five senators are expected to run for president this time around. Sen. Bernie Sanders kicked off his Democratic candidacy in Vermont this week, and Sen. Lindsey Graham (R) of South Carolina is expected to announce next Monday.

But it’s not the numbers that pose a challenge for Senator McConnell. It’s the behavior.

Former Sen. Richard Lugar (R) of Indiana, who ran for president in 1996 along with three other Republican senators – including then-majority leader Bob Dole, who won the nomination – describes a “more collegial atmosphere” among his group of candidates and in the Senate generally. 

He doesn’t recall any “head-on collisions" such as last weekend’s between Paul and McConnell, which he calls “very serious.”

“The personalities involved in ’95 and ’96 were perhaps not as combative as the current group,” he says. “By that I mean simply we respected each other.”

Mr. Lugar mentions that regular attendance at caucus meetings helped generate respect. Paul didn't show up at last week's GOP caucus gathering on the Patriot Act.

Senators aspiring for higher office could make things tough for McConnell by their presence on the campaign trail – and absence from the chamber, perhaps depriving him of the 60 votes he needs to do anything of consequence in the Senate. That scenario hasn’t happened yet, but the campaigning senators are definitely missing votes (though Paul is managing a high rate of participation).

The presidential candidates can also throw up parliamentary blockades, such as the one erected by Paul on Saturday. The libertarian firebrand strenuously objects to the mass gathering of phone data under the Patriot Act, and he has made it a signature issue in his bid for the presidency.

Presidential hopefuls can also disrupt the Senate by introducing contentious amendments that buttress their campaigns, such as one by Senator Rubio a month ago that sidelined – for a time – a bipartisan deal on the Iran bill.

Rubio insisted that the Senate vote on his amendment, which would have required Tehran to recognize Israel’s right to exist as part of any final nuclear agreement between Iran and international powers. To avoid that “poison pill,” McConnell was forced to shut down the amendment process – contradicting his own promise of a more open and deliberative Senate.

“These senators have been a thorn in McConnell’s side,” says Sarah Binder, a congressional expert at the Brookings Institution, a Washington think tank.

The leader has tried to manage the challenge in different ways, with mixed results. He's taken issues right up to a deadline in an attempt to force consensus, expanded and cut off debate, and jawboned senators behind closed doors at caucus meetings. He's also tried to work out deals with lawmakers individually.

“Senator McConnell and his caucus have made it pretty clear that they’re not going to tolerate these guys hijacking the floor,” Manley says. “Cruz, in particular, understands that” – referring to the senator who led the way to a partial government shutdown in 2013, earning the hostility of many GOP senators in return.

Given that it’s only May, that the candidates are likely to stay in the race for some time, and that some big issues lie ahead, McConnell is going to continue encountering pushback from the presidential candidates, Ms. Binder says.

Will disagreement over highway funding precipitate something, she wonders? What if the US Supreme Court strikes down subsidies for the Affordable Care Act – will that get Senator Cruz back in the game on Obamacare?

“I don’t think McConnell’s challenges are diminishing anytime soon,” she says.

As for the Patriot Act, of which key provisions are set to expire on June 1, McConnell may be the one who has to back down. The surveillance legislation with the most support in the Senate is the House’s USA Freedom Act, which passed overwhelmingly in that chamber and which missed a 60-vote threshold by only three votes in the Senate. 

One of them was McConnell’s.