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Former comedian Al Franken apparently is done cracking jokes.

In the past month, Franken, the junior Democratic senator from Minnesota has publicly slugged it out with a GOP senator, privately rebuked another one and on Thursday took the unusual step of shutting down on the Senate floor a longtime member of his party's caucus: Sen. Joe Lieberman.

Unlike during his days on "Saturday Night Live," no one is laughing.

"Sen. Franken is certainly not making friends on either side of the aisle," GOP strategist Ron Bonjean, a former Capitol Hill aide, told Fox News.

Franken joined the Senate in July after winning an eight-month political and legal battle with Republican Norm Coleman over an election that nearly ended in a tie. Despite his freshman status, Franken hasn't shied away from confrontation with senior lawmakers, some of whom have spent decades in the chamber.

Lieberman, for example, who was first elected to the Senate in 1988, was the Democratic vice presidential candidate in 2000 and currently chairs the powerful Homeland Security and Governmental Affairs Committee.

By contrast, Franken, since becoming the Democrats' 60th vote in the Senate, has taken seats on a few committees, including health and judiciary, where he voted for the confirmation of Sonia Sotomayor to the Supreme Court.

As a comedian, Franken cultivated an image as an irreverent performer and satirist. As a senator, Franken is cultivating an image as a confrontational lawmaker with no regard for seniority in a chamber that embraces it.

That appeared to be on full display Thursday as Franken was presiding over the Senate. When Lieberman, I-Conn., asked for some more time to finish speaking about amendments he planned to offer to the Senate health care bill -- a routine request -- Franken refused to grant the time.

"In my capacity as the senator from Minnesota, I object," Franken said.

"Really?" Lieberman said. "OK."

Lieberman, taken aback, said he'd submit the rest of his statement in writing.

Click here to watch the exchange.

Lieberman currently is the target of liberal wrath over his opposition to a government-run insurance plan in the health care bill. But Franken's spokeswoman, Jess McIntosh, said that the Minnesota senator wouldn't allow Lieberman to continue because time limits were being enforced by Senate leaders rushing to finish a defense spending bill and get to the health bill.

Republican Sen. John McCain of Arizona, came to his friend Lieberman's defense, saying he'd never seen such a thing occur. "I must say that I don't know what's happening here in this body, but I think it's wrong," McCain said on the floor.

Franken's in-your-face behavior shouldn't come as a surprise to those who have followed his career as an author and radio host. Franken has made sport of launching angry -- and sometimes juvenile -- attacks on prominent conservatives, such as Rush Limbaugh -- one of his best-selling books is titled "Rush Limbaugh Is a Big Fat Idiot" -- and members of the Bush administration.

In the summer, Franken reportedly savaged T. Boone Pickens at a Democratic policy lunch for helping fund the Swift Boat Veterans for Truth attacks against Sen. John Kerry in the 2004 presidential race.

Franken vowed before joining the Senate to keep his head down, work hard and win over his colleagues. But so far, winning over his colleagues hasn't been going so well.

Franken's first legislation, which created a pilot program to provide service dogs for wounded veterans, passed without controversy. But it was Republican opposition to Franken's anti-rape amendment to the defense bill that brought out his not-so funny side.

Franken's amendment, which would prevent the Pentagon from working with contractors that require employees to settle discrimination claims, including ones of sexual assault, in arbitration rather than court, passed 68-30. All 30 no votes were cast by Republicans, with the other 10 party members supporting it.

The Republicans who voted against the amendment were portrayed as rape sympathizers by liberals. That prompted an opinion article in a local newspaper by Tennessee GOP Sens. Bob Corker and Lamar Alexander, whose defense of  their opposition was based partly on the argument that the measure would leave contractors more exposed to lawsuits.

Franken reportedly confronted each senator separately to dispute their column and lost his temper with Corker in a sharp exchange.

On Monday, Franken initiated a sharp exchange with Sen. John Thune, accusing the South Dakota Republican of distorting the facts in his health care chart that purported to show how the Senate bill would hike taxes immediately while delaying the benefits.

"We are entitled to our own opinions. We're not entitled to our own facts," Franken said, adding with his voice rising that if Thune is going to hold up a chart, he "better include the benefits that do kick in right way."

Thune fired back, questioning whether Franken understood his point that tax increases start right away while benefits don't kick in until 2014.

"If the senator missed the point, I can get the chart out again," Thune said.

Franken said, "I asked a question senator. I yield to you for a question. I'm asking a question."

Thune eventually walked out on the argument.

Click here to watch the exchange.