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A wave of corruption arrests and investigations is roiling Democratic politicians, posing a potential image problem in an election year.

The latest were a pair of arrests earlier this week, snagging Charlotte Mayor Patrick Cannon, who later resigned, and California state Sen. Leland Yee. The latter involved a tangled web of allegations including claims that the gun control-pushing lawmaker tried to connect an undercover agent with an international arms dealer.

So far, these cases are confined to the state and local levels, so it remains to be seen whether Democrats running in the congressional midterms will be tarnished.

In fact, the only major arrest of a U.S. congressman since the beginning of 2013 was that of a Republican, Florida Rep. Trey Radel, who was convicted for cocaine possession and resigned early this year. Each party typically is careful to throw stones when the other side finds itself on the wrong side of the law, because corruption and other misbehavior is a bipartisan problem.

For every Anthony Weiner, there's a Mark Foley.

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But since Radel's October arrest, the bulk of the corruption cases have involved Democrats.

In California alone, Yee's case marked the third arrest or conviction in as many months of a state Democratic official.

State Republicans, who have been struggling to regain their political footing, have sought to capitalize on the wave of criminal charges as a way to undo Democrats' dominance in the Legislature. Republicans have repeatedly tried to expel Sen. Rod Wright after he was convicted of perjury and voter fraud in January for lying about his legal residence in Los Angeles County. Democratic leaders have blocked those efforts. The state Senate, though, voted Friday to suspend all three of the lawmakers in trouble.

The other, Sen. Ron Calderon, was indicted on federal corruption charges in February. Prosecutors say Calderon accepted about $100,000 for himself and family members in exchange for promoting legislation to expand Hollywood tax credits and protect the interest of a hospital that benefited from a provision of the workers' compensation law.

Then came Yee, whose alleged activities were more befitting Hollywood than his San Francisco district.

The criminal complaint contained dramatic details about Yee's alleged efforts to connect an undercover agent with a firearms dealer.

"Do I think we can make some money? I think we can make some money," the senator allegedly said in one of the meetings.

The cases, while involving local politicians, have put powerful Democrats in an awkward position.

U.S. Sens. Barbara Boxer and Dianne Feinstein of California joined a growing list of officials on Thursday in distancing themselves by demanding Yee's resignation. The Democratic leader of the state Senate, President Pro Tem Darrell Steinberg, warned Yee to resign or face suspension by his colleagues, saying "he cannot come back."

Cannon, meanwhile, was ensnared in an FBI sting and faces federal corruption charges alleging he accepted more than $48,000 in cash, airline tickets, a hotel room and a luxury apartment from undercover agents posing as real estate developers and investors. Cannon, while not a household Democratic name, led the city that hosted the Democratic National Convention in 2012.

On top of that case, Rhode Island House Speaker Gordon Fox said Saturday he was resigning from leadership and would not run for re-election, a day after federal and state authorities raided his Statehouse office and home as part of a criminal investigation that they would not detail.

The Friday raids were carried out by the U.S. attorney's office, FBI, IRS and state police. Boxes of evidence were carried off after agents spent hours at both his home and office. Officials will not say whom or what they are investigating.

The 52-year-old Providence Democrat, who became the nation's first openly gay House speaker in 2010, said he planned to serve out the remainder of his term through the end of the year, but that "my personal focus going forward will be on my family and dealing with the investigation."

Meanwhile, in the shadow of the U.S. Capitol, the mayor of the District of Columbia, a Democrat, is facing his own problems. A U.S. attorney claimed earlier this month that Mayor Vincent Gray knew about an illegal, $668,000 "shadow campaign" that helped propel him into office four years ago. Despite denials from the mayor, who has not been accused of a crime, the revelation further damaged him ahead of next week's primary.

"I think the question politically is whether it becomes emblematic of the national party," said Mary Katharine Ham, a Fox News contributor. "And that, to some extent, depends on media coverage. In, for instance, 2006, there was the drumbeat against Republicans was this culture of corruption; and that, to a large extent, was effective because it was so consistently covered in the media."

The Associated Press contributed to this report.