Second term Colorado Senator Wayne Allard, arguably the most endangered Republican whose seat is up in 2008, has long been rumored to be pondering retirement. According to M.E. Sprengelmeyer of the Rocky Mountain News, these are rumors no longer.

Sen. Wayne Allard said today he will honor his term-limits pledge and leave at the end of 2008, creating a replacement fight that should turn Colorado into one of the country's biggest electoral battlegrounds.

Democratic Rep. Mark Udall, who has all but declared his candidacy for the Senate, will come into this race with significant strengths -- including the fact that, as of the end of November, he had close to $1.3 million in his campaign coffers. Greg Giroux of CQPolitics.com runs down the potential Republican field.

Potential Republican candidates, should Allard decide to retire, include one current and two former House members.

The active incumbent is Tom Tancredo, who was elected to his fifth term last November in the conservative-leaning 6th District outside of Denver. One of the nation's most vocal opponents of illegal immigration, Tancredo is mulling a candidacy for the 2008 Republican presidential nomination.

One of the ex-members on the Senate race prospect list is Rep. Scott McInnis, who represented the western 3rd District from 1993 to 2005 and who has $939,000 remaining in a campaign fund that could be transferred to a new Senate campaign account. The other is former Rep. Bob Schaffer, who represented the eastern 4th District from 1997-2003 and who lost the 2004 GOP Senate primary to Coors.

Given that Colorado Democrats, in the past two cycles, have picked up the governorship, both chambers of the state legislature, a Senate seat and two Congressional seats, and that the Democratic Party has selected Denver to house its nominating convention in 2008, there is no doubt that this will be one of the top targets for the strategists and activists trying to extend the Democratic majority in the United States Senate. Chuck Schumer, chairman of the Democratic Senatorial Campaign Committee, has said as much recently. While I'm not, at this juncture, ready to call the race for the Democrats, as has Markos, it is clear that this will be an extremely difficult seat for the Republicans to defend next year. At the least, this race is now a toss-up and perhaps even has a slight Democratic lean.

Update [2007-1-15 17:54:16 by Jonathan Singer]: By most measures, Udall is fairly progressive, though various voting scorecards paint at least somewhat different pictures of his position within the Congress. According to CQ, Udall voted with his caucus on party-line votess 92 percent of the time during the second session of the 109th Congress. Looking at his voting pattern during the first session of the Congress, National Journal gave him a liberal ranking of 68.7 (71 on economic issues, 67 on social issues, 67 on foreign policy) while he earned a "B" on the Drum Major Institutes middle class report card, voting in favor of the Republican immigration bill but voting "correctly" on all other measures listed.

Update [2007-1-15 18:15:29 by Jonathan Singer]: According to a subsequent article from the Rocky Mountain News, Tancredo may not, in fact, run next fall.