Just weeks ago, it seemed inconceivable the Republicans could win control of Congress this fall. Not anymore. Almost by the day, Republicans are sensing fresh opportunities to pick up ground.

Just Wednesday, former Indiana Sen. Dan Coats announced he would try to reclaim his old seat from Democrat Evan Bayh, who just a year ago had been a finalist to be Barack Obama’s running mate. And Republicans nationwide are still celebrating Scott Brown’s January upset to take Edward Kennedy’s former seat in Massachusetts.

A Republican takeover on Capitol Hill is still a long shot. But strategists in both parties now see at least narrow paths by which the Republicans could win the House and, if the troubled environment for Democrats deteriorates further, possibly even the Senate. “The likelihood is that Democrats hold the House and Senate,” says former Sen. Bob Kerrey, a Nebraska Democrat who calls party members’ gloomy forecasts overstated. Still, he adds: “Democrats have got their hands full trying to navigate through unprecedented economic turmoil and two wars. And there’s no question that there’s anger out there.” Says former Democratic Sen. Bob Graham: “It would be surprising if Democrats lost power. But anything in politics is possible. And if the economy’s still in the tank ... it’s going to be difficult for Democrats.” With 10 months to go, 2010 is shaping up in one sense to be a traditional midterm election for a new president: The out-of-power party is poised to gain seats in both houses. The question now is whether it will be a historic election with Republicans actually seizing power in Congress.

The Republicans would have to gain 40 seats in the 435-member House, ten in the 100-member Senate — a tall order no matter how upset voters are. But still ...

In the Senate, two Democratic seats are all but gone. North Dakota’s Byron Dorgan is retiring, and the Democrats don’t have anyone to challenge the Republican candidate, Gov. John Hoeven. Democrats also failed to recruit their top candidate in Delaware. Vice President Joe Biden’s son eschewed a run against Republican Mike Castle. For a Republican takeover, incumbent Democrats also would have to lose in Colorado, where appointed Sen. Michael Bennet hasn’t run statewide and faces a primary; Nevada, where Senate Majority Leader Harry Reid is unpopular but has a hefty bank account; Arkansas, where Sen. Blanche Lincoln suffers from representing a Republican-leaning state; Pennsylvania, where party-switching Sen. Arlen Specter is extraordinarily vulnerable; and Illinois, where a dogfight is certain for Obama’s old seat.

Republicans would have to hold on to all the Senate seats they have now, hardly a sure thing. And the Republicans also would have to beat incumbents in New York, where no Republican has emerged to challenge appointed Sen. Kirsten Gillibrand, and Connecticut, where Democrat Richard Blumenthal is comfortably leading all Republican contenders in polls. If all that somehow happens, the tipping point could be either in Indiana or in California.

“Every state is now in play,” California Sen. Barbara Boxer said one day after the Massachusetts election. It was a frank recognition that no Democrat is safe — not even a three-term liberal with bunches of money in a solidly Democratic state. Not coincidentally, when Obama had a televised question-and-answer session with Democrats on Wednesday, the senators given prominent face time included Boxer, Reid, Bayh, Bennet, Lincoln, Gillibrand and Specter. In the House, Democrats hold a 256-178 advantage with one vacancy. But 49 Democrats are in districts that Republican presidential candidate John McCain won in 2008. And many are freshmen who rode into power on Obama’s coattails in an election that saw a voting surge by minorities and youths.

Obama won’t be on the ballot this time, and he has a poor track record so far when it comes to turning out his 2008 backers for fellow Democrats. House Republicans have their own challenges. In more than 50 districts, divisive Republican primaries are certain to drain bank accounts and force Republicans into taking positions that could be troublesome come the general election.

In many cases, “tea party” candidates — grass roots conservatives who oppose Obama’s spending programs — are running to the right of establishment-endorsed Republicans, casting them as too moderate.