Presidential hopeful Sen. Sam Brownback, R-Kan., steps off his campaign bus at a stop in Adel, Iowa. Brownback kicked off his summer road trip Monday, a 1,200-mile, four-day, 27-stop tour through Iowa.

Topeka ? U.S. Sen. Sam Brownback, a conservative Republican running for president, has missed nearly 40 percent of his Senate votes this session.

Many of those absences stem from campaigning in Iowa in preparation for that state’s leadoff presidential caucus in January and the Iowa Straw Poll, which is Saturday.

Brownback’s campaign did not return a telephone call or e-mail seeking comment about his voting. In a June teleconference with reporters, Brownback said he was trying to do the best he could at balancing his campaign and Senate duties.

And, he said then, some of his missed votes were a consequence of a trip he took to Iraq and Afghanistan and a visit to Greensburg to inspect tornado damage.

Brownback has missed 123 of 310 Senate votes this session, or 39.7 percent, according to a Washington Post database.

That ranks him as the third-most-absent senator behind Tim Johnson, D-S.D., who suffered a brain hemorrhage on Dec. 13, 2006, and hasn’t returned to the Senate, and John McCain, R-Ariz., another presidential candidate, who has missed 48.1 percent of votes.

Behind Brownback are three more presidential candidates: Joseph Biden, D-Del., at 25.2 percent; Christopher Dodd, D-Conn., at 23.9 percent; and Barack Obama, D-Ill., at 19 percent, according to the database. Sen. Hillary Clinton, D-N.Y., another presidential contender, missed 3.5 percent of votes and Kansas’ other senator, Pat Roberts, a Republican, missed 3.9 percent.

Brownback has missed votes on the Iraq war, minimum wage, the budget and ethics reform.

Last month, he issued a news release praising the passage of legislation to help recovery efforts in tornado-ravaged Greensburg, but he wasn’t there to vote for it; he was campaigning in Iowa.

The Kansas Democratic Party has criticized Brownback’s campaigning on Senate time.

“Sam Brownback continues to shirk his duties as a U.S. senator so he can campaign in Iowa,” state Democratic Party Chairman Mike Gaughan said. “But skipping a vote that would help the people of Greensburg is unacceptable. And taking credit for that is downright misleading.”

Brownback and Roberts said Brownback worked on the legislative amendment aimed at benefiting Greensburg. The legislation passed easily, 89-4, and was part of a larger bill that included funding for border control and homeland security programs.

Joe Aistrup, head of the political science department at Kansas State University, said voters can excuse a presidential candidate who is a member of Congress from missing some votes, but missing 40 percent is excessive.

“Kansans elected him and, as a consequence, they expect him to be there,” Aistrup said. “On the other hand, most Kansas voters recognize that a person running for president is going to miss a few votes. The question is what is a reasonable number to miss.”

After Saturday, Aistrup said, Brownback may have more time to tend to his duties at the Capitol.

That’s the day of the Iowa Straw Poll, an early test vote where Republicans buy tickets for their supporters to vote for them.

If Brownback finishes lower than third place, his presidential campaign could end, Aistrup said.

“He better come in first or second,” Aistrup said. “Mitt Romney and Brownback are pulling out all stops, but Brownback needs to come out of the pack of secondary candidates.

“Iowa is farm country, and Brownback is a farm-state senator,” he said. “If he is not going to do well in Iowa, he is not going to do well anywhere. Third place may be acceptable.”