With nearly five months to go until Election Day, Republican hopes of retaking the Senate have dimmed and they're privately lamenting their lost opportunity. Until just a few weeks ago, Republicans considered winning a Senate majority a long shot but by no means out of reach. But the euphoria over Scott Brown's victory in Massachusetts in January seems a distant memory now, especially after the latest round of primary results last week.

Primary victories by Carly Fiorina in California and Sharron Angle in Nevada bolstered a growing national narrative that Republican candidates are lightweights, or too outside the mainstream, to survive in the fall, and that could harm even top tier Republicans.

"There's now a path to 'acceptable losses' for Democrats," notes one cautiously optimistic Democratic strategist.

"I totally see how the number stops at five to seven [Republican pickups]" says a Republican consultant, speaking of an optimistic scenario for the GOP.

"Nevada is the one place that fundamentally changed," says a top GOP consultant, who now predicts Harry Reid will be re-elected. "I don't think Angle can win personally."

Professional GOPers are split over whether California Republicans elected the best possible candidate in Carly Fiorina, but broadly speaking there's little thought given any longer to the idea that Barbara Boxer's seat is still in play.

The Republicans still have obvious pick ups. Barring a major shakeup, North Dakota, Indiana, and Arkansas all lean strongly Republican. In Delaware, Rep. Mike Castle (R) has a commanding lead over Democrat Chris Coons. But Coons is a tireless campaigner, and will soon be drawing out the big guns, including a forthcoming fundraising visit from Vice President, and former Delaware Senator, Joe Biden.

A tier below that, though, and the picture becomes murky. Colorado is anybody's guess, as is Pennsylvania. The top Republican strategist worries about what happens if Pennsylvania "becomes a race between a decorated Navy Admiral [Democrat Joe Sestak] and a Wall Street guy [Republican Pat Toomey]."

Colorado still has a primary to resolve, but if Democratic incumbent Michael Bennet defeats his challenger Andrew Romanoff, polls show him closing in on Republican rival Jane Norton.

Illinois features a race between a flawed Republican candidate--Mark Kirk, who's been caught exaggerating his military record repeatedly--and a flawed Democratic candidate--Alexi Giannoulias, whose family owns a bank that was recently seized by the Feds. But Kirk's missteps have acutely harmed him, according to recent polls, leading the Democratic firm Public Policy Polling to conclude "It's hard to see this race as anything but a pure tossup at this juncture but in Illinois a race between a flawed Democrat and a flawed Republican is probably going to end up in the Democratic column, and Giannoulias' 5 point gain relative to Kirk in the 10 weeks reflects that."

Democrats in Washington state (Murray), Wisconsin (Feingold), and Connecticut (Blumenthal) are safe for now. And Republicans have a couple vulnerabilities of their own.

Popular Florida Governor Charlie Crist is running an increasingly liberal campaign in Florida as an independent against Republican Senate hopeful Marco Rubio and Democrat Kendrick Meek.

And then there's Louisiana, where for the first time since a major sex scandal, Sen. David Vitter (R) will have to face the voters. For the time being, he remains solidly ahead. If you believe the Republican firm Magellan strategies, he leads Democrat Charlie Melancon by 20 points. But a Democratic PPP poll due out tomorrow has Vitter up by only 9 (46-37). And that's before the Democrats have taken aim at Vitter's troubled past.

In a sneak preview for TPM of the Democrats' strategy, a Louisiana strategist says Dems and their surrogates will both directly remind voters of Vitter's transgressions, and use that history, along with his voting record, to dominate the female vote.

"I think you'll see Democrats and outside groups, including disaffected Republicans, members of the Tea Party movement, reminding folks about Vitter's scandal," the Democratic strategist told me.

The revelation that Vitter had frequented prostitutes came at the best (or least harmful) possible time for him, years before his next election. But once voters are reminded of the details, Democrats hope they'll be able to capitalize, particularly with women.

"[T]here will be devastating television ads and mailers pointing out that Vitter voted against equal pay for women, he voted against a law designed to help rape victims, to make sure rape victims get their day in court, he voted against SCHIP--in Louisiana called LACHIP--and consistently voted against female nominees," the strategist added.

Add to that the fact that the general election field is likely to be peppered with conservative underdogs--including a libertarian candidate and a Tea Party-backed independent--all of whom should take votes away from Vitter, and it's not hard to imagine that race becoming competitive in the end.