By Bob Benenson, CQ Staff

Since the previous Jigsaw Politics provided a list of the five House seats rated by CQ Politics as most vulnerable, it’s time to survey the Senate — and as with the House Top 5, it brings more bad tidings for our Republican readers out there.

The five Senate seats most likely to flip parties (with links to more details on the races) are:

• Virginia, where Democrat Mark Warner, a popular governor from 2002 to 2006, is heavily favored to succeed retiring five-term Republican Sen. John W. Warner (no relation). Mark Warner’s 2001 win for governor stanched a long-running Republican trend in Virginia and set the stage for further major Democratic gains this decade. His political strength is based largely on his reputation for having fixed a fiscal shortfall he inherited from his predecessor, Republican James S. Gilmore III — who happens to be his Republican opponent in this year’s Senate race. Gilmore, a conservative who barely edged out an even more conservative candidate at the state Republican nomination convention, argues that Warner trumped up a fiscal crisis to raise taxes. CQ Politics rates the race as Democrat Favored, meaning this is a likely pickup for the challenging party.

• New Mexico, a swing state, where six-term Republican Pete V. Domenici ’s decision not to seek re-election has created a golden opportunity for a Democratic takeover. Five-term Rep. Tom Udall , who was unopposed for the Democratic nomination, has opened up a big lead in polls over the Republican nominee, strongly conservative three-term Republican Rep. Steve Pearce . Pearce won a narrow victory in the June 3 primary over the state’s third House member, Heather A. Wilson , whose image as a less-hardline conservative than Pearce led some GOP strategists to view her as potentially a stronger contender against Udall. Running in a state that is split very evenly between the parties, Pearce is staking his hopes on persuading voters that Udall’s House record is too liberal. This race is rated Leans Democratic, which means Udall has an edge in a contest that still is highly competitive.

• New Hampshire, where first-term Republican Sen. John E. Sununu ranks as the incumbent most vulnerable to defeat this year. Sununu faces Democratic former Gov. Jeanne Shaheen in a tough rematch of their 2002 race. He won that contest by 4 percentage points, but, oh, how times have changed in this longtime bastion of Yankee Republicanism. Democrats have long been gaining ground: George W. Bush won New Hampshire by just 1 point in 2000, and the state flipped in 2004 — the only one to go from Republican to Democratic in Bush’s two elections — by giving Kerry a 1-point edge. State Democrats, aided by strong voter dissent toward the Iraq War, then had one of their biggest years ever in 2006, capturing both of the state’s U.S. House seats and control of both state legislative chambers as Democrat John Lynch won a landslide victory for a second two-year term as governor. Shaheen has enjoyed big leads in polls so far, though the outcome ultimately is expected to be close. CQ Politics currently rates this and the final two races on this list as No Clear Favorite.

• Colorado, where Democratic gains over the past few years would have endangered two-term Republican Sen. Wayne Allard had he run for re-election. Instead, he is retiring, and the Democratic nominee to succeed him, five-term Rep. Mark Udall , has held the lead in recent polls. The state still is closely divided politically and Republicans say they are confident that their candidate, conservative former Rep. Bob Schaffer, will hold the seat by proving to voters that Udall, whose political base is in the liberal college town of Boulder, is too far left for Colorado. Schaffer, though, has been hindered by news reports that he was one of several House members who took trips that turned out to be financed by later-convicted influence peddler Jack Abramoff. Udall, the son of the late Arizona Rep. Morris K. Udall, is a cousin of New Mexico Senate hopeful Tom Udall , whose father is former Arizona congressman and Interior Secretary Stewart Udall.

• Mississippi, where interim Republican Sen. Roger Wicker , appointed to his seat last December, faces competition from a well-known Democrat, former Gov. Ronnie Musgrove, in a special election to fill the final four years of resigned Republican Trent Lott’s unexpired term. As in most of the South, conservative Mississippi long ago shed its old-school Democratic traditions and swung hard toward the Republican Party. But the national downturn for the GOP has had its effect even here, as boldly illustrated by the victory for Democrat Travis W. Childers May 13 in the special election to succeed Wicker in the 1st Congressional District seat he had held for 13 years. State voters’ ingrained Republican voting habits in statewide races, which make Republican presidential nominee John McCain a solid favorite to carry Mississippi, give ample hope to supporters of Wicker, who is known as a mild-mannered and diligent lawmaker. But Democrat Musgrove, though he lost his 2003 bid for re-election to Republican Haley Barbour , is known statewide, while Wicker is well-recognized in just one of the state’s four House districts. Republican strategists have tried to open up some breathing space for Wicker by hammering Musgrove for past campaign donations he received from figures now involved in a state political corruption scandal.

Yes, just as in the House Top 5, all of the Senate races we see as most likely to change hands are for Republican seats hotly pursued by Democrats. In fact, if this were a list of the Top 10 takeover targets, nine would be Democratic bids to take over Republican seats.

The choice of Mississippi for the fifth slot is a close call over the race in Minnesota, where first-term Republican Sen. Norm Coleman is in a tossup race with Democrat Al Franken, the entertainer and liberal activist — and where the contest would be rendered even more unpredictable by the likely entry of Jesse Ventura, the former governor and one-time professional wrestler.

Just a cut below are three races rated by CQ Politics in the competitive Leans Republican category. Ted Stevens , the longest-serving Republican senator in history and for many years a dominant political figure in Alaska, is facing a tough challenge from Democratic Anchorage Mayor Mark Begich, enhanced by the controversy over Stevens’ ties to state business figures embroiled in a sweeping political corruption scandal. Oregon Sen. Gordon Smith, who increasingly has cast himself as a Republican moderate, nonetheless is at risk against Democratic state House Speaker Jeff Merkley in a state that generally leans Democratic. And Maine’s Susan Collins , another Republican moderate from a Democratic-leaning state, will have to make the most of her strong job approval ratings to deflect a serious challenge from six-term Democratic Rep. Tom Allen .

The only at-risk Democratic seat that would make a Top 10 list is the one two-term Sen. Mary L. Landrieu is defending in conservative-leaning Louisiana. Her contest is in CQ Politics’ competitive Leans Democratic category, but even this race says something about the unsteady state of the Republican Party nationally. In order to find a candidate deemed willing and able to seriously challenge Landrieu, Republican officials resorted to persuading state Treasurer John Kennedy to switch his affiliation from Democratic to Republican.

Lest you think that the avowedly nonpartisan CQ Politics site is showing a Democratic bias, this outlook is upheld by an unlikely source: Nevada Sen. John Ensign , who as chairman of National Republican Senatorial Committee has the unenviable job of coordinating his party’s effort to hold its ground in the Senate races this year.

At a press breakfast June 12 sponsored by the Christian Science Monitor, Ensign listed the 10 races he deemed most competitive, and Louisiana was the only Democratic-held seat on his list. The rest of the states overlapped with our list save one: Ensign at the time excluded the Mississippi race but included the North Carolina contest, currently rated Republican Favored by CQ Politics, in which first-term Republican Sen. Elizabeth Dole is challenged by Democratic state Sen. Kay Hagan.