Senator Marco Rubio(R-FL) announces his candidacy for the Republican presidential nomination on April 13, 2015.National Journal

The five senators now in the mix for the 2016 presidential campaign face a grim reality: Just three of their predecessors have gotten elected directly to the White House from the Senate.

The pitfalls for senators seeking the presidency are many. A presidential campaign is a full-time job and senators still have their constituents to think about, committees to chair, and prized legislative goals to see through to their ends. Not to mention a conflict-happy media that will scrutinize missed votes, colleagues who need their "ayes" and "nays," and, of course, the whole problem of sleeping and spending time with family.

While then-Sen. Barack Obama managed to overcome those hurdles against fellow Sen. John McCain in 2008, and John F. Kennedy made the leap in 1960, the other six senators who won their party's nomination in the last six decades all failed in the general election.

With that track record in mind, what advice do former candidates and their strategists have for the current crop of hopefuls?

"Advice? I'm the loser!" McCain said, laughing in the basement of the Capitol last week. "Why should they review any of my advice? 'Here's how you lose....'"

But as several of his colleagues have jumped into the 2016 fray, McCain said he's talked to each of them about balancing their Senate careers with their presidential aspirations and what to expect on the campaign trail. "They all come see me. What the hell? Why not?" McCain said.

THE RAIN IN SPAIN ...

Even though they seem to talk for a living, many senators running for president need to learn how to speak all over again. The kind of "legislative-ese" common to floor speeches in the Senate (just turn on C-SPAN for a few minutes) won't cut it on the campaign trail, said Dan Schnur, who ran communications for McCain's campaign in 2000.

When you're building and disseminating a national campaign message, you need "short, declarative sentences," said Jim Jordan, who ran Sen. John Kerry's 2004 campaign and consulted on Sen. Chris Dodd's presidential effort in 2008. Candidates need not only to captivate audiences on the campaign trail, but to be able to answer debate questions in a short period of time—and in language that voters will actually understand.

But senators, particularly "those who have been in the Senate for a while," have forgotten how to talk like real people, Jordan said. Retraining them in "real human speech" is often the first step for a campaign.

"There's an artificial grandiosity to their speech which just grates on average folks," Jordan said of clients in the Senate. "They say things like 'I voted for it before I voted against it.'"

Schnur pointed to the same issue among senators who have sought the White House in the past. "Every senator running for president should be instructed to never, ever, ever refer to a piece of legislation by its bill number," Schnur said.

DANCE WITH THE ONE THAT BRUNG YA

The most obvious problem for senators-turned-presidential candidates is one with which Sens. Ted Cruz, Lindsey Graham, Rand Paul, Marco Rubio, and Bernie Sanders are already dealing: when to stay in Washington and when to campaign.

With so many candidates in the field, particularly now, senators need to spend time in the early primary states meeting voters and traveling the rest of the country raising money. At the same time, they still have jobs to do and a state to represent. Constituents, and the media, can be unforgiving of missed votes.

"If you're going to run for president, your constituents have to know that you're going to miss votes, and they'll make a judgment," McCain said. "And one of the ways they'll make a judgment is how well you'll do in seeking the nomination. If you're a complete failure, they'll say, 'Well why'd you miss all those votes?' If you get the nomination, they'll say, 'See, good work.'"

As for which votes you skip and which you show up for, McCain and others aren't exactly helpful. "I think on a case-by-case basis," McCain said.

"The scheduling challenge is always there," Jordan said. "It's not that hard to get from Manchester back to Washington. Des Moines [is] a little bit trickier. But since [Senate Majority Leader Mitch] McConnell doesn't have a vested interest in keeping his senators off the campaign trail, it's a challenge, but not a debilitating one."

Will there be votes that put presidential candidates in a difficult spot? Sure. Just look at the Iraq war vote and the 2004 and 2008 campaigns. But it's important that senators continue to vote their hearts. "I never had a conversation ... with any presidential aspirant directly about the effect of a vote on a presidential race. That doesn't mean that's not a part of the calculus," Jordan said. "It's hard to find many senators whose voting patterns change radically in the two years leading up to a presidential run."

As the campaign heats up, candidates will have to take more and more time away, and that means putting some legislative goals aside, at least for the time being. Luckily, senators still have the Senate floor to work with. "Passing a bill on an issue of major concern to voters can be helpful, but not that much more than simply talking about that issue," Schnur said.

I'M LATE! I'M LATE! I'M LATE!

"It's very difficult having two full-time jobs," Jordan said.

Candidates need to make time to maintain their sanity. In McCain's case, his wife, Cindy, was very protective of his schedule and consistently checked in to make sure he had time to rest, Schnur said. "When you're campaign staff, it's very, very easy to look at an empty hour on a schedule and automatically fill it. It takes a loyal adviser or a very engaged spouse to protect against that instinct," Schnur said.

"I think Fred Thompson had a great line on this when he ran for president," he added. "He said never let a 25-year-old run the schedule for a 65-year-old candidate."

WASHINGTON WHO?

One of the biggest questions senators have to grapple with in a presidential campaign is how to attract national voters while serving in Congress, a body that has just a 19 percent approval rating. "There's the lecturing at fundraisers that the Senate's not doing this or that right," Jordan said.

"It's often hard to run against Washington from inside Washington," Schnur said, pointing to former Sen. Bob Dole, who resigned from office during his presidential campaign, and then-Vice President Al Gore, who set up his headquarters in Nashville to avoid the stink of Washington.

McCain tried to get away from Washington in 2000 by arguing that the federal government was corrupted and needed reform. And who better to fix it than a man who knew it so well? "But even so, once [McCain] won the New Hampshire primary, Governor [George W.] Bush began referring to him as 'Chairman McCain' and began talking about him as the chair of a very powerful Senate committee," Schnur said.

McCain lost. But his opponent next time around found a stronger message: I'm new enough to Washington that I understand it, but "I haven't been there long enough to get infected," Schnur said. "The Obama model is the right one."

Given the junior status of most of the senators running in 2016, the Obama model is one they can imitate. "They can say: 'I just got here, I'm horrified by what I saw. And I want to change it,'" Schnur said.

IT'S NOT ALL BAD

The one major advantage senators have over the rest of the field could be even more significant this cycle than in many recent presidential races: their superior grasp of foreign policy.

Even senators with little real foreign policy experience get the benefit of the doubt because of their position. "Voters assume that if you serve in a national body, you're going to have a better understanding of international issues," Schnur said. "So while they generally think more highly of governors and senators, a governor without experience in Congress has to play catch-up on national security."

Jordan agrees. "The term 'senator' does imply to voters "¦ achievement, experience, knowledge about public affairs."

Most senators, Jordan notes, have at least "passing knowledge" of almost every policy issue that will come up in a presidential race. "That's a huge advantage too," Jordan said, particularly in debates.

Whether that's enough to overcome the disadvantages of their ties to Washington and the demands on their schedules remains to be seen. Despite Obama's and McCain's successes over the last eight years, it doesn't mean it's getting any easier for senators on the road to the White House.

"Give Obama credit," Schnur said. "Just because this happened once every 50 years" doesn't mean it'll happen again.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.