ANNAPOLIS, Md. (WJZ) — One day after Maryland’s longest serving senator surprises everyone announcing she won’t run for reelection, the list of candidates who may want to replace her continues to grow.

Derek Valcourt first looked at the long list of possible contenders, and he already has an update.

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In a surprise to many, former Governor Martin O’Malley says no thanks to a run for Mikulski’s Senate seat. That leaves the race to replace her wide open for a host of other possible contenders.

Many of them are Maryland House Democrats—from Elijah Cumming to Dutch Ruppersberger to Chris Van Hollen to wealthy Western Maryland Congressman John Delaney. They’re all at least saying they’ll think about it.

“It would be a really interesting primary for people like you, reporters, and political junkies like me,” said Don Norris, UMBC public policy director.

No matter who’s in, the Senate campaign could come with a big price tag. Campaign ads for governor last year in the primary alone exceeded $11 million.

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Maryland’s last Senate race saw Ben Cardin reelected in 2012 after the candidates spent nearly $17 million.

With Republicans hoping to pick up a Senate seat long held by the Democrats, it’s possible Maryland’s 2016 race could approach spending levels seen when Elizabeth Warren and Scott Brown waged a $70 million Senate battle in normally blue Massachusetts.

UMBC public policy director Don Norris says how much gets spent for Maryland’s Senate race all depends.

“Who the Republicans field, if they field a very serious, well-funded candidate, the Democrats are going to have to match that. So yes, it could be very expensive,” said Norris.

For now, no Republicans have formally expressed interest in running.

We should have a much better idea of who is running in the next six to nine months as fundraising efforts ramp up. The deadline to file for the race isn’t until next January.

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Former Lieutenant Governor Anthony Brown is also reportedly considering a possible run for Mikulski’s Senate seat.