It's the first of April, the first quarter filing deadline has passed and the national Senate landscape is beginning to shake out. Since our last look at the races up for election this year, several tiers are becoming evident. Three first-tier targets, look almost certain to flip to the opposing party's control. Four second-tier seats are in serious danger of flipping control. And two third-tier seats have the incumbent party favored, but at least vulnerable. If either party benefits from a huge wave this year, a few other seats could provide close races, but it will take a massive wave to dislodge anyone below the ninth spot.

All this can, and will, change in the months to come. But seven months before election day, here's where the exchange stands:

Races We Considered For The 10 Spot: Mississippi, where appointed Senator Roger Wicker could face a tough contest against Democratic ex-Governor Ronnie Musgrove. But Musgrove's tangential involvement in a lawsuit in Georgia that alleges corporate executives improperly funneled money to his campaign could be a big problem. Kentucky, where Mitch McConnell, the most visible Republican not employed in the White House or named McCain, could face a backlash from voters who just kicked out a GOP governor. Ironically, McConnell could be better suited by associating himself with Washington Republicans than with anything that looks like Ernie Fletcher's GOP, regardless of the fact that the Bluegrass State's Republican Party is more McConnell's than anyone else's. And New Jersey, where Frank Lautenberg could conceivably have a bad moment in a debate and shake Garden State voters' confidence enough to elect a Republican. Lautenberg would have made the ten spot had businessman Andrew Unanue, who entered the race last week, not had such a difficult launch.

Races we dropped since December: Mississippi.

Races we added since December: North Carolina.

10. North Carolina (R-Dole): Republican Elizabeth Dole has not had the easiest first term on record. Her stint as chair of the National Republican Senatorial Committee was nothing short of disastrous, and though she has fundraised well, some believe she could be vulnerable, especially against a top-tier challenger. Democrats tried to woo Governor Mike Easley and his wife, Mary, but neither were interested. Instead, national strategists hope State Senator Kay Hagan makes it through the primary against investment banker Jim Neal. Hagan has raised good money and could at least keep Dole off the trail on behalf of other Republicans. Still, Hagan faces a serious uphill battle. (Last: Not ranked)

9. Oregon (R-Smith): Republican Gordon Smith should, by any account, be in a heap of trouble. He represents an increasingly Democratic state in what should be a heavily Democratic year. But thanks to a primary in which State House Speaker Jeff Merkley and attorney Steve Novick are forcing each other to the left, Smith could end up winning another term by a wider margin than had Democrats succeeded in avoiding a primary. Smith himself has moved to the middle, voicing opposition to the war in Iraq and distanced himself from the Bush Administration, making him more palatable to his state's war-opposing moderates and independents, a bloc that plays a bigger role than in most states. (Last: 6)

8. Maine (R-Collins): At the opening of the third tier, Democrats are going to need a wave to take out Susan Collins. The Republican incumbent is very popular, though she has a few important factors working against her: The presidential contest will likely bring out Maine's generally Democratic electorate, and Democrats signed their top potential recruit, Rep. Tom Allen. But Collins leads by a wide margin in the only two polls conducted in the state, and support from her close friend Joe Lieberman can only help among the plethora of independents around Maine. Collins is ranked ahead of Gordon Smith, of Oregon, only because of Allen's apparent strength as a candidate. (Last: 8)

7. Minnesota (R-Coleman): Running against a former Saturday Night Live comedian isn't supposed to be this hard. But Republican Senator Norm Coleman will not have an easy time against Al Franken, especially now that the Democrat's path to the nomination is mostly clear. Recent polls have shown the two rivals within the margin of error against each other, and both are raising big bucks. Coleman kicked off his campaign by taking aim at Franken, signaling that the race will be one of the more contentious in the country this year. If Coleman keeps the spotlight on Franken, Coleman can keep his job. One gets the sense that if the race becomes more about the Republican Party that will hold its convention in St. Paul to nominate John McCain, Coleman will win. If the race becomes more about the GOP that elected President Bush twice, Franken could be a Senator. (Last: 7)

6. Louisiana (D-Landrieu): Incumbent Mary Landrieu is virtually the only Democrat on the GOP's target list. While recruits from several other states passed on their races, the GOP got the candidate they want with State Treasurer John Kennedy. Still, Republican voters in the state might not be wedded to Kennedy; he only switched from the Democratic Party last year. And Landrieu's performance after Hurricane Katrina has even won her endorsements from some Republicans. Landrieu remains the favorite in the race, but, given the state's new GOP nature, not by much. (Last: 4)

5. Colorado (R-Open): Poll numbers continue to show the race closer than conventional wisdom suggests. Democratic Rep. Mark Udall continues to lead every survey, but Republican former Rep. Bob Schaffer is keeping the race tight. Udall has a cash advantage, and Democrats have made big gains in the states in recent years. Independents in the state have broken left lately, and if they continue to head that way, the Democrat will win. In a competitive state during a competitive presidential year, the Senate race to replace outgoing Republican Wayne Allard could determine whether Colorado has turned blue, or whether it's still a purple state. (Last: 5)

4. Alaska (R-Stevens): Since our last ranking, the Democratic Senatorial Campaign Committee has landed its top recruit, Anchorage Mayor Mark Begich. The party has high hopes for taking out incumbent Stevens due to his involvement in a scandal surrounding an oil services corporation, and a December poll showed the Democrat leading by six points. That poll also showed Stevens with a seriously upside down approval rating. Thanks to Begich's entry, the race moves to the head of the second-tier pack, but only because of Alaska's hard-Republican tilt and the nagging feeling that Stevens may not be the Republican on the ballot in November. (Last: 9)

3. New Mexico (R-Open): Republican Reps. Heather Wilson and Steve Pearce are increasingly moving right as Democratic Rep. Tom Udall, with a cleared primary field, is already talking to general election voters. Pearce, largely seen as the candidate farther to the right and less electable statewide, took a victory in a recent party convention. With help from Governor Bill Richardson, who is widely popular in the state, Udall should be the next senator from New Mexico. (Last: 2)

2. New Hampshire (R-Sununu): Despite a few American Research Group polls that showed the race between Senator John Sununu and former Democratic Governor Jeanne Shaheen close, recent surveys, including a new one from ARG, shows Shaheen well ahead. Given that Democratic Governor John Lynch has avoided any serious Republican challenger, the GOP will have a more difficult time motivating their voters. The x-factor for Sununu: John McCain is virtually the state's third Senator, and his presence at the top of the ticket could help. But New Hampshire gets ranked ahead of New Mexico because 2006 showed a bigger swing toward Democrats in the Granite State than in the Land of Enchantment. (Last: 3)

1. Virginia (R-Open): Despite some Republican efforts to find another candidate with a shot at beating former Democratic Governor Mark Warner, the party still looks like it will go with former Governor Jim Gilmore. Polls have shown Warner leading his gubernatorial predecessor by a two-to-one margin. Without a major slip from Warner -- his lead in that poll was twice as large as George Allen's over Jim Webb in a Mason-Dixon poll when Allen called a Webb campaign staffer a "macaca" -- Democrats will win the Commonwealth. (Last: 1)