Sen. Marco Rubio, R-Fla., speaks at the Defending the American Dream summit hosted by Americans for Prosperity at the Greater Columbus Convention Center in Columbus, Ohio, on Aug. 22, 2015.(Photo: Paul Vernon, AP)

WASHINGTON — Congress faces critical decisions this fall on legislation to keep the government open after Oct. 1, a deadline to raise the debt ceiling, and a long-overdue highway bill.

What's not clear is whether Florida Sen. Marco Rubio will participate in the debates and votes that will determine the fate of those issues.

Rubio, a candidate for the GOP presidential nomination, has missed 77 of 263 roll call votes this year, through Wednesday, an absentee rate of nearly 30%. That's more than any other senator, according to a USA TODAY review of votes cast through Wednesday.

Since June 1, the freshman senator has been absent for 60% of votes, as he's stepped up his appearances at campaign events and fundraisers. He's skipped votes on amendments to a massive education bill, changes to defense policy legislation, and a short-term extension of the federal Highway Trust Fund.

The second- and third-ranking senators on the absentee list are GOP presidential candidates as well. Sen. Lindsey Graham of South Carolina has missed 62 votes this year (24%), and Sen. Ted Cruz of Texas has missed 59 votes (22%), according to the review.

The two other senators running for president rarely miss votes. Independent Bernie Sanders of Vermont — running for the Democratic nomination — has missed nine votes (3%), while Republican Sen. Rand Paul of Kentucky has missed only three (1%).

Paul is seeking re-election to his Senate seat while he campaigns for the presidency. Rubio also is up for re-election next year but he's decided not to run for another term.

Aides to Rubio, who campaigned in the key early primary state of New Hampshire this week, say it's not unusual for senators seeking the White House to spend significant time away from their day jobs starting the year prior to the election.

They cite the cases of three former Democratic senators — Hillary Clinton (who missed 23% of votes in 2007), President Obama (who missed 38% in 2007), and Secretary of State John Kerry (who missed 62% in 2003).

Rubio spokesman Alex Conant said campaigning for the nation's highest office is time-consuming and can't be left to surrogates. But that doesn't mean Rubio is shirking his duties, Conant said.

"He has returned to the Senate whenever his vote would be decisive, is regularly briefed on issues before his committees, and keeps up on the important constituent work that his Senate staff does," Conant said. "As he travels the country talking about his agenda to help the middle class, there will be no doubt where he stands on any important issues before the Senate and the nation."

Rubio canceled a fundraiser in Minnesota Thursday and returned to Washington to vote for a resolution of disapproval on the nuclear agreement with Iran.

Lawmakers running for the White House are always challenged to balance campaign demands against their responsibilities to constituents back home.

"If you do well, and make significant progress (as a candidate), then people are rather proud of you," said Arizona Sen. John McCain, the 2008 GOP presidential nominee who was criticized for missing votes while on the campaign trail. "If you fail to gain any traction, then they're going to be asking why you wasted all that time in Iowa and New Hampshire."

Recent national polls show GOP support for Rubio hovering around 5%.

There's no rule book on how much time senators who run for president should devote to their day jobs. Generally, they promise to show up in Congress for key votes, including votes where they would be key to the outcome.

Paul said his top priority is serving the voters who elected him.

The taxpayers of Kentucky pay for me to come to the Senate, deliberate and vote," he said. "I think it's an important responsibility."

South Dakota Sen. John Thune, the third-ranking Republican in the Senate, said party leaders keep in touch with the four GOP senators running for the White House to tell them when they might be needed on key votes.

He said none of this year's absences have determined the outcome of a vote. But Thune, who flirted with a presidential run in 2012, said missing votes to campaign could reverberate negatively among voters.

"If you're running as a governor or a senator, people are going to evaluate your performance in how you've done and whatever it is you're doing today," he said. "I think attentiveness to the work here and being engaged in it is pretty important."

Five senators are running for president in 2016. Here's the number and percentage of votes each one has missed this year (of the 263 cast through Wednesday):

Sen. Marco Rubio, R-Fla.: 77 votes (29.3% of total)

Sen. Lindsey Graham, R-S.C.: 62 votes (23.6%)

Sen. Ted Cruz, R-Texas: 59 votes (22.4%)

Sen. Bernie Sanders, I-Vt. (running for the Democratic nomination): nine votes (3.4%)

Sen. Rand Paul, R-Ky.: three votes (1.1%)

Source: USA TODAY research

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