Republican takeover of the Senate is no longer impossible in 2010. If Scott Brown wins in the special election Tuesday for the Senate in Massachusetts, it would mean Republicans would have to net 10 seats to take control. If he loses, 11 would be needed.

Either way, polls in state after state show Republicans have a shot of either capturing the Senate outright or gaining enough seats to be able to block liberal initiatives by denying Democrats the votes to halt filibusters.

In states where they have credible candidates, Republicans are ahead or tied. Should Brown win – proving a Republican can win in even the bluest of states – Republicans who today figure they can’t win are likely to change their minds and run. This is especially true in states without strong Republican candidates now — Indiana, New York, Wisconsin, Oregon, and Washington.

Here’s what the latest polls show in eight states with Senate seats held by Democrats:

Arkansas. Blanche Lincoln trails by 3 to 6 points the four Republicans vying to run against her.

Colorado. Appointed senator Michael Bennett is running behind Republican Jane Norton, 49 percent to 37 percent, in a fresh poll.

Connecticut. Chris Dodd trailed both Republican candidates, Rob Simmons and Linda McMahon, before dropping out. His exit caused the polls to flip. Now Democrat Richard Blumenthal is ahead of both Republicans by more than 20 percentage points. This is the only heavily contested state where Republicans trail badly.

Delaware. An open Democratic seat where Representative Mike Castle leads state attorney general Beau Biden, 45 percent to 39 percent.

Illinois. An open seat, once held by President Obama, finds Democratic state treasurer Alexi Giannoulias ahead of Representative Mark Kirk, 42 percent to 39 percent.

Nevada. Senate Democratic Leader Harry Reid continues to lose ground against two Republicans. He trails Danny Tarkanian 50 percent to 36 percent and Sue Lowden 48 percent to 36 percent.

North Dakota. Another open seat, this one due to Byron Dorgan’s retirement. Republican Governor John Hoeven leads three possible Democratic candidates by 23 percentage points or more.

Pennsylvania. Arlen Specter, who switched parties last year to become a Democrat, is running behind Pat Toomey, 46 percent to 42 percent. Toomey also leads Specter’s primary foe, Representative Joe Sestak.

To summarize, Republicans are in the lead in six of the races for Democratic seats, trail narrowly in one, and by a lot in one. That’s a pretty good starting point in January for Republicans.

Winning Democratic seats won’t help much, however, if Republicans don’t hold their own open seats, six of them:

Florida. Both Governor Charles Crist and former state house speaker Marco Rubio are leading Democratic Representative Kendrick Meek— Crist by 6 percentage points, Rubio by 14.

Kansas. It’s not certain who the candidates will be. It is all but certain that a Republican will win.

Kentucky. Here, too, Republican secretary of state Trey Grayson and eye doctor Rand Paul are ahead of both possible Democratic candidates by at least 6 percentage points.

Missouri. Secretary of state Robin Carnahan leads Representative Roy Blunt, the former House Republican whip, by 46 percent to 44 percent.

New Hampshire. Kelly Ayotte, the Republican state attorney general, is ahead of Representative Paul Hodes by 49 percent to 40 percent.

Ohio. Republican Rob Portman has surged ahead of the Democratic candidates, leading Lieutenant Governor Lee Fisher, 44 percent to 37 percent, and secretary of state Jennifer Brunner, 43 percent to 40 percent.

Republicans have a way to go before challenging Democrats for control of the Senate, but they’re far ahead of where they expected to be only six months ago. Then, Democratic control seemed to be unassailable. Now, the political wisdom is there are no permanent majorities.

Update: Barbara Boxer now faces a tough re-election challenge in California from any of three Republicans. A new Rasmussen Poll finds Boxer with small leads over ex-Hewlett Packard CEO Carly Fiorina (46 percent to 43 percent), former Representative Tom Campbell (46 percent to 42 percent), and state senator Chuck Devore (46 percent to 40 percent).

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