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Longtime Rep. Barney Frank, D-Mass., announced Monday he is not seeking re-election, saying that redistricting has made it too strenuous to continue to campaign.

The 16-term lawmaker, whose name is emblazoned on the banking reform law that passed Congress last year, had long been rumored to be ready for retirement. He said Monday that he actually decided "tentatively" to retire after passage of the law, serving out one more term, but when Republicans won the 2010 midterm he decided he didn't want to be a lame duck so didn't announce his plans until now.

Frank said he now wants to do some combination of writing, teaching and lecturing, but will not become a lobbyist.

One of the best parts of retiring is "I don't have to pretend to be nice to people I don't like," he said, adding that he will continue to be an advocate of public policy, for instance, on gay rights issues and debating the Defense of Marriage Act against opponents like former House Speaker and 2012 Republican presidential candidate Newt Gingrich.

Feeling more unleashed than usual, Frank also said he found it striking that so many Republicans would consider Mitt Romney, the former Massachusetts governor, as their nominee since he flip-flops.

"He would be the best thing to happen to the Democratic Party since Barry Goldwater," Frank said.

Frank was previously chairman of the House Financial Services Committee but is now ranking member since Democrats lost the majority in the 2010 midterm election. The Dodd-Frank law, a contentious set of provisions that Republicans say add layers of regulatory burdens without preventing potential future meltdowns, was made in response to the near collapse of the banking industry in 2008. Among other actions, it created a Consumer Financial Protection Bureau to oversee access to banking products and required listing ratios of executive pay to median employee salaries.

Frank acknowledged that the financial fallout of Fannie Mae and Freddie Mac's near collapse came as a surprise.

"I, like many others, did not see the crisis coming," he said, going into a long disposition about how in 2005 he did try to get legislation passed to prevent unqualified homeowners from getting loans, but was stopped by then-House Majority Leader Tom Delay, R-Texas.

"When Tom DeLay ran the House, the majority did not have much to say so until 2007, I had virtually no impact," Frank said, adding that the first bill he passed when he became chairman of the Financial Service Committee was regulated Fannie and Freddie. He said his actions were then excoriated by The Wall Street Journal and others.

Frank, 71, was first elected to the House in 1980, and is one of the first lawmakers to announce he is homosexual.

"Barney Frank has exemplified true leadership over his more than 30 years in the U.S. House of Representatives, said Joe Solmonese, outgoing president of Human Rights Campaign and a former campaign staffer for Frank. "As the first openly gay member of Congress, Barney defied stereotypes and kicked doors open for LGBT Americans. Repeal of 'don't ask, don't tell' and passage of the Matthew Shepard and James Byrd Jr. Hate Crimes Prevention Act would never have happened without his leadership. ... America, Massachusetts and LGBT people are better off for Barney Frank's service."

Frank's tenure hasn't been without scandal. More than two decades ago, the lawmaker was reprimanded by the House for using his congressional status on behalf of a male prostitute whom he had employed as a personal aide, including seeking dismissal of 33 parking tickets.

"I should have known better. I do now, but it's a little too late," Frank said at the time.

Democrats offered their praise for the outgoing lawmaker.

"No one's ever doubted for a minute what Barney Frank thinks or where he stands, and if you weren’t sure, trust me, he’d tell you. That’s the special quality that has made Barney not just beloved and quotable, but unbelievably effective as an advocate and a legislator," said Sen. John Kerry, D-Mass.

"On behalf of the DCCC, I thank Barney Frank for his distinguished service in Congress.," said Democratic Congressional Campaign Committee Chairman Steve Israel. "He's led our caucus and our country to a better place, fighting for opportunity, fairness, and equality. ... Congress will not be the same without him."

Not everyone was sorry to see Frank announce he's going.

Americans for Limited Government President Bill Wilson said that Frank ignored the warning signs of Fannie and Freddie's impending fall, defending the government sponsored enterprises weven when he was aware of the undercapitalization that was required for loans they guaranteed. Wilson added that Fannie and Freddie were essentially ignored during the financial reforms even though they were "ground zero" for the crisis.

"Frank leaves behind a disastrous record that will have consequences for years if not decades to come. His departure comes about 20 years too late," Wilson said. "To his departure, American taxpayers say good riddance."

Republicans made a concerted effort to knock off Frank in the last election cycle, nominating Sean Bielat, a 35-year-old businessman and former U.S. Marine, who had made waves, but had little chance of knocking off a powerful incumbent in a strongly Democratic leaning district.

Indeed Frank's remarks about redistricting did not indicate that he was concerned about a new challenger, merely that he was not interested in trying to introduce himself to new constituents.

"I don't want to be torn between a full-fledged campaign in a district with 325,000 new people and my obligation to the existing district and that is reinforced by the fact that I would have a hard time going to 325,000 new people, some of them in areas that I am not very familiar with like the Blackstone Valley, and say, 'by the way I would like to be your Congressman for two years,'" he said.

President Obama won 61 percent of the vote in Frank's previous district in 2008. Sen. John Kerry, the home state senator who ran for president in 2004, pulled in 62 percent in the district. Reportedly, with Frank's departure, one notable conservative who may be encouraged to run is former Red Sox pitcher Curt Schilling.

Frank is now the 17th House Democrat to flat-out retire or step aside to seek other office. Republicans have announced seven retirements this cycle. He is also the second House Democrat to announce his retirement in three days and the second Massachusetts Democrat to say he's stepping down. Rep. Charlie Gonzalez of Texas announced his retirement over the weekend. Rep. John Olver decided a few weeks ago not to run for another term.

Fox News' Chad Pergram contributed to this report.