Democrat Russ Feingold (left) and Republican Sen. Ron Johnson (right) are in a rematch of their 2010 race. Credit: Journal Sentinel files

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If you've seen U.S. Sen. Ron Johnson on TV or at a town-hall meeting recently, you've probably noticed something about him.

Wisconsin's senior senator has become Mr. National Security.

"What I have been focusing my efforts on as chairman of the Senate Committee on Homeland Security and Government Affairs is our vulnerabilities," Johnson told MSNBC on Dec. 9. Last month, his campaign launched a digital ad touting Johnson's record on national security issues.

He didn't always have such a keen interest in the subject.

In his first four years in office, Johnson missed 60% of the hearings held by the homeland security committee and the subcommittees to which he was assigned. Even according to numbers supplied by Johnson's campaign, the state's senior senator made it to only 83 hearings out of a total of 207 from 2011 to 2014.

Among the hearings Johnson missed were one on homegrown terrorism, one on terrorist travel 10 years after 9-11 and three on border security. On at least two occasions in 2011, Johnson made it to fundraisers on the same day he missed a homeland security hearing.

"Chairman Johnson is the worst kind of hypocrite," said Kory Kozlowski, executive director of the state Democratic Party. "He says national security is his most important issue. But until 2015, he barely showed up to work on critical committee hearings regarding our homeland security."

Johnson is being challenged by Democrat Russ Feingold, a former senator.

Brian Reisinger, a spokesman for Johnson, said the attack is off the mark.

Numbers provided by Johnson's team show that Johnson made it to 47 of 50 hearings by the homeland security committee since he was named chairman last year.

If you include his attendance at work sessions — in which members vote on bills — over the past five years, Johnson went to 167 hearings out of a total of 298. That's a 56% attendance rate.

"Unlike many other senators, Ron does more than briefly drop into hearings to simply say he was there; he spends the time needed to hear testimony and ask tough questions," Reisinger said. "Ron is known in the Senate as a real workhorse."

Reisinger noted that former U.S. Sen. Joe Lieberman, a Connecticut Democrat, once praised Johnson for his strong attendance record on the homeland security committee back in 2011.

If anyone is being hypocritical, Reisinger suggested, it is Feingold.

That's because Johnson's campaign calculated that the Middleton Democrat made it to only 50% of the hearings held by the U.S. Senate Foreign Relations Committee and his subcommittees from 2005 to 2010, including several hearings on Iran's nuclear program. If work sessions are included, Feingold could not have gone to more than 59% of all 328 committee meetings.

Feingold's team disputes the accuracy of those numbers.

"It's totally hypocritical for Feingold's political henchmen to attack Ron's attendance since Sen. Feingold's was comparable, reflecting the fact that many committees meet at the same time and perfect attendance is impossible," Reisinger said.

There is some truth to that.

Anyone who has flipped on C-Span — and who doesn't spend their free time that way? — has seen committee chambers filled with empty seats and one or two bloviating congressmen on an obscure topic.

"There is simply not enough time in the day most of the time" to attend all hearings, said Joshua Huder, a senior fellow at the Government Affairs Institute at Georgetown University.

Members of the House and Senate have to prioritize which meetings they consider most important, Huder said. A typical congressman has 10 to 15 committee and subcommittee assignments.

But that doesn't stop attendance records from becoming campaign fodder. Huder called the subject "low hanging fruit."

"I don't know of any race where it has been the sole issue," Huder said. "If you're trying to paint someone as lazy or out of touch and not fulfilling their duties, if they have a low attendance record and have missed votes," you can build a narrative around that.

And some have.

In 2014, then-U.S. Sen. Mary Landrieu presented herself as a leading voice for Louisiana on energy issues in the U.S. Capitol. But Landrieu, a Democrat, came under attack for missing nearly 70% of the full energy committee hearings and those for the subcommittee on which she sat.

She later lost her seat.

More recently, U.S. Sen. Ted Cruz of Texas, who is a leading Republican candidate for president, has been sharply criticized for being MIA at hearings held by the Senate Armed Services Committee. Cruz was the only committee member with an attendance record below 50%.

"It's absolutely essential," said former U.S. Sen. John Warner, a Virginia Republican who blasted Cruz in Politico last year. "I spent 30 years there and attended as many as I could possibly attend."

In Johnson's case, he was known for his seemingly single-minded focus on the national debt during his first run for office in 2011 and in his first four years in office. His website was packed with dense charts discussing the country's out-of-whack government spending.

Reisinger, Johnson's spokesman, said the senator sees the problems of the national debt and national security as closely linked.

"National security has always been one of Ron's priorities, and part of keeping our country safe is addressing our nearly $19 trillion federal debt," Reisinger said.

Instead of focusing on Johnson's attendance, his aide suggested that it was more important that Johnson had helped push through 55 bipartisan bills during his tenure as chairman of the homeland security committee, including 16 measures signed into law by President Barack Obama.

By contrast, Feingold never was named a committee chairman during his 18 years in Washington, D.C.

The Democratic Party's Kozlowski emphasized that Johnson's attendance numbers on the homeland security committee were relevant because he is the one trying to make national security a key campaign issue. It is generally believed that Republicans fare better when foreign policy and national security are the most important issues in a race.

But Kozlowski said Johnson wasn't interested in the subject until just recently. The topic has become a hot one nationally since the terrorist attacks in Paris and San Bernardino, Calif., late last year.

"If he really cared that much about keeping us safe," Kozlowski said,"he'd have done his job when the voters weren't looking, not just when his job was at risk."

Bill Glauber of the Journal Sentinel staff contributed to this report.