For the first time since May 19, the Buzz is offering a ranking of the six U.S. House seats that are most vulnerable to a party switch this fall.

Most lawmakers on our list saw their ranking jump around a bit, but in general, the difference between first place (the most vulnerable) and sixth (less vulnerable) has shrunk, due in part to continued uncertainty about wide-open GOP primaries to pick challengers of endangered Democratic Reps. Suzanne Kosmas and Alan Grayson.

As always, the rankings are based on interviews with a range of political practitioners and independent observers. We consider the state's other 19 House seats to be safe for the party currently in power, though if any show signs of life, we'll add them to our rankings as we update them every month or so.

1. Rep. Suzanne Kosmas, D-New Smyrna Beach. (Previous ranking: 1) Kosmas’ underlying vulnerability hasn’t changed – she’s still a freshman representing a modestly GOP-leaning district who first voted against the Democratic health care bill and later for it, irritating both sides in the process– but the Republican field remains fractured, with weak fundraising. Former Ruth's Chris Steak House CEO Craig Miller, Winter Park Commissioner Karen Diebel and state Rep. Sandy Adams have all loaned their campaigns large amounts of money but still trail Kosmas in cash on hand by a considerable margin. Each of the Republicans will need to spend a good chunk of their limited cash on the wide-open Aug. 24 primary before having to regroup for the general election. So while the national Republican trend this fall will help whoever wins, none of the Republicans shows signs of being an incumbent-killer at this point.

2. Open seat being vacated by Mario Diaz-Balart, R-Miami. (Previous ranking: 5) In something of a rarity for this strong GOP year, the leading Democrat running for this GOP-held open seat, 2008 nominee Joe Garcia, had a much better two months than did the leading Republican, state Rep. David Rivera. Rivera was outraised in the quarter, $728,000 to $518,000; he faced flak from fellow Republicans for his ties to a businessman who favors easing trade restrictions with Cuba; and he saw a Tallahassee house he co-owns with former House Speaker Marco Rubio slip very publicly into foreclosure. Add to these the continuing allegations of corruption within the Florida GOP, growing voter annoyance at Tallahassee politicians, and the loss of inevitability that Rubio will be Florida’s next Senator and suddenly Garcia -- who’s largely kept his head down – has a real shot at winning. The open seat, created when Mario Diaz-Balart switched districts to seek the seat being vacated by his retiring brother Lincoln, is fairly competitive between the two parties. But Rivera has been a formidable political force, so we're not ready to write him off.

3. Rep. Ron Klein, D-Boca Raton. (Previous ranking: 6) One of the most stunning fundraising numbers anywhere this quarter– not just in Florida – was the $1.4 million raked in by Allen West, the GOP challenger to Klein, a second-term Democrat who raised only about one-third as much over the same period. The African-American ex-Army colonel raised much of his money from out-of-state donors, thanks to a well-developed network of supporters who have responded to his firebrand conservative style. West now has a warchest of $2.2 million, not far behind Klein’s own (and not-too-shabby) $2.9 million. The key question is whether big money, energetic grass-roots support and a Republican tide can enable West to oust an incumbent in a district that’s generally far more moderate, ideologically and temperamentally, than the challenger is.

4. Rep. Alan Grayson, D-Orlando. (Previous ranking: 2-tied) Grayson is the Florida Democrat who Republicans love to hate, but can the GOP actually knock him off? Grayson’s blunt provocations have excited liberals nationally, turning him into a fundraising machine. While his haul this quarter declined to a comparatively mortal $328,000, Grayson still has four times as much banked cash as his nearest GOP rival, and he can always dip into his own deep pockets if he needs to. Money aside, Grayson took a PR hit when news reports questioned whether he was secretly supporting a Tea Party entity that could help split the GOP vote in his district as well as others across the state. (He denies it.) Still, before taking on Grayson, the GOP must get past a messy primary. The establishment choice, former state House speaker and state Senate Majority Leader Dan Webster, has raised the most money and is a major figure in the district, but he’s also a consummate Tallahassee insider, and he has yet to put away a large field of rivals, including state Rep. Kurt Kelly, traffic-signal businessman Bruce O'Donoghue, 2008 primary contender Todd Long and tea party activist Patricia Sullivan. Whoever wins, Grayson seems to have the tenacity to be able to survive an unfavorable environment.

5. Rep. Allen Boyd, D-Monticello. (Previous ranking: 2-tied)  Boyd, a conservative "Blue Dog" Democrat representing a Republican-leaning district, isn’t out of the woods yet thanks to the likelihood of a strong GOP wave, but he looks more comfortable now than he did two months ago. Boyd raised about 20 times as much as his primary challenger from the left, state Sen. Al Lawson, and more than twice as much as his leading Republican rival, funeral-home owner and political neophyte Scott Southerland. Boyd will still have to worry about Democratic turnout in an off-year election; as we said in May, this is precisely the kind of seat that tipped from Democratic to Republican in 1994. So while we’ve lowered Boyd on our rankings this month, his vulnerability could easily rise again as Election Day nears.

6. Open seat being vacated by Rep. Adam Putnam, R-Bartow. (Previous ranking: 4) This is arguably the sleepiest race on our list, despite the likelihood of an intriguing three-way general election between a Democrat (Polk County elections supervisor Lori Edwards, a moderate, or possibly Navy veteran Doug Tudor, a liberal), a Republican (former state Rep. Dennis Ross) and a Tea Party candidate (Randy Wilkinson, an iconoclastic Republican who has been elected to county offices three times). Ross has raised the most money -- $170,000 for the quarter, with $440,000 in the bank – but none has been a fundraising powerhouse, and the candidates have barely engaged each other as of yet. All things being equal, this district should stay Republican, especially in a GOP wave year, but the lack of activity and the complicated general-election dynamics suggest that it’s premature to call this race for any candidate.