They may have left Capitol Hill, but many former members of Congress retain active campaign accounts—some of them holding millions of dollars that continually stoke rumors of political comebacks.

A few decades back, former members of Congress could take their campaign cash with them, for personal use, when they retired. That avenue has long since been closed off, but former federal candidates are still free to hoard what campaign funds they had left and use it to donate to charities, candidates, and state or national party operations.

Though leftover campaign funds can't be used for strictly personal purposes, they do come with perks, namely leverage and attention. Since Republican Sen. Dan Coats of Indiana announced he'd retire in 2016, for example, all eyes are back on former Sen. Evan Bayh and the $10 million he still has in a federal campaign account. Since almost the day the Democrat retired in 2011, that account has fueled speculation that Bayh might one day return to office.

Longtime Bayh adviser and former Indiana Democratic Party Chairman Dan Parker has repeated that Bayh—who now works as a strategic adviser for the Washington-based law and lobbying firm McGuireWoods LLP—will not run for Coats's seat. But Parker has also reiterated that Bayh is still keeping the door open for future possibilities.

While he has no immediate plans to reenter the political arena, Bayh can still play a role in the upcoming election. He has given nearly $1.6 million to the Indiana Democratic Party, for example, which comprises most of his election-fund spending since he left office. But based on past trends, it is unlikely that Bayh will have a significant impact on the 2016 elections.

Bayh has donated to a handful of past Senate and House campaigns, including $4,500 to Indiana Democrat Joe Donnelly's Senate bid in 2012. But when it comes to contributions to the national party, the Democratic Senatorial Congressional Committee shouldn't expect a large check. Bayh's committee gave more than $30,000 to the DSCC in 2011 but hasn't appeared on its donor list since. Meanwhile, interest keeps replenishing Bayh's account as he spends and donates from it.

Bayh is hardly the only former member sitting on a boatload of campaign cash. Here are some of the other ex-senators and ex-representatives with the most money left over:

Former Rep. Marty Meehan, D-Mass. Meehan left the House in 2007, after 15 years, to serve in as chancellor of the University of Massachusetts, Lowell. He was recently named president of the entire University of Massachusetts system, making a political comeback unlikely. But just in case, Meehan has more than $4.4 million in his campaign account. He has slowly been unloading his fund in recent years via a few hundred thousand dollars' worth of donations to charities and candidates per year. Still, Meehan actually has the most cash on hand of any House campaign committee right now.

Former Rep. Joe Kennedy II, D-Mass. Kennedy, who served in Congress for more than a decade, has been out of Congress since 1999, but Kennedy still has $2.6 million in cash on hand in his campaign account. A steady stream of interest and investment income from Goldman Sachs replenishes the account even as the political dynast doles out a few political contributions per election cycle—including $1,800 to family member Bobby Shriver's campaign for Los Angeles County supervisor last year.

Former Sen. Tom Harkin, D-Iowa. Harkin only left Congress three months ago, but he still has more than $2.3 million left in his account. He can still use campaign dollars to wind down his office—a former member can do this up to six months after leaving. But the main destination for his money looks like it will be the Drake University institute that bears his name. Last year, Politico reported that Harkin turned down Democratic Party requests for that money as his colleagues battled futilely to keep his seat and their Senate majority.

Former Rep. Michele Bachmann, R-Minn. Bachmann, who unsuccessfully ran for the 2012 Republican presidential nomination, retired from Congress last year after serving for eight years. While her presidential campaign account is empty, her congressional account still has $1.6 million in cash on hand. What she'll do with that stockpile is anyone's guess, but it puts her account among the largest belonging to former members.

Former Sen. Ken Salazar, D-Colo. Salazar served in the Senate for less than a term before President Obama appointed him to run the Interior Department, where he stayed until 2013. A sometimes-rumored future gubernatorial candidate, Salazar has about $1.2 million in his federal account and moved back to Colorado to open a Denver office for the international law-firm WilmerHale.

Former Rep. Mark Foley, R-Fla. Foley served in Congress for a decade before resigning in 2006 amid allegations that he sent suggestive emails to teenage boys serving in the congressional-page program. But he has entertained the idea of a political comeback, and he'd start it with about $1.2 million leftover in his bank account. Like Bayh, Foley has taken a "never slam a door on the future" approach to maintaining his political coffers.

Former Rep. Cliff Stearns, R-Fla. Stearns served in the House for 24 years before losing a GOP primary. Now, he works as a senior adviser for the public-relations firm APCO Worldwide. Stearns has nearly $1.5 million left in campaign funds—money that might have come in handy in that surprise loss to Ted Yoho in 2012—and that's after donating $50,000 to his alma mater, George Washington University, in March.

Former Rep. Jerry Costello, D-Ill. Costello spent about 25 years in the House before retiring in 2013. In his first term out of office, he was one of the top contributors among former members of Congress in the last election, spreading hundreds of thousands of dollars from his campaign account to congressional candidates, party committees, super PACs, former Illinois Gov. Pat Quinn, and his own son (an Illinois state legislator). But Costello's contributions still left him with more than $1.1 million stockpiled, and he could have a similar impact in the upcoming election.

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