By Greg Giroux, CQ Staff

With a hefty war chest and a lead in the polls, Colorado Democratic Rep. Mark Udall ’s prospects of taking over the Senate seat of retiring Republican Sen. Wayne Allard appear to be brightening.

CQ Politics is changing its rating of the high-profile Colorado Senate race to reflect a slight edge for Udall, who is facing Republican former Rep. Bob Schaffer.

By shifting the rating of the Colorado Senate race to “Leans Democratic” from “No Clear Favorite,” CQ Politics now considers Udall as a narrow front-runner in a highly competitive race that had been previously classified as a toss-up. Udall, who represents the Boulder area, and Schaffer, who represented Colorado’s eastern plains from 1997 through 2002 and sought Colorado’s other Senate seat in 2004, are unopposed in their party’s primaries on August 12.

Though CQ Politics does not base its race ratings changes primarily on polling data, it’s unmistakable that Udall has moved out to a consistent lead in a series of polls, including a nine-point advantage in a Public Policy Polling survey that was conducted earlier this month.

Udall’s edge can be attributed to other factors. The national political environment continues to be more problematic for the Republicans than the Democrats. In Colorado, Democrats made big gains in the 2006 election. Barack Obama at the moment is at least an even-money bet to defeat John McCain in Colorado, which in 2004 backed President Bush over Democratic nominee John Kerry by 5 percentage points. Republicans still outnumber Democrats on the voter registration rolls in Colorado, though the gap is narrowing and political independents are now more numerous than either Republicans or Democrats.

Both Udall and Schaffer will be vying for the votes of political independents, though the two men do have plenty of disagreements on policy issues. Udall has had a mostly liberal voting record and Schaffer had a mostly conservative voting record.

Udall has an early edge in fundraising over Schaffer. As July began, Udall had $4 million left to spend, compared to $2.8 million for Schaffer, according to updated campaign finance reports that were filed last week. Udall’s cash-on-hand advantage narrowed in this year’s second quarter because Udall spent about three times as much as Schaffer did in the three-month period that ended June 30.

The Colorado Senate race is the third in which CQ Politics presently gives the non-incumbent party the edge over the defending party. In all three cases, the Democrats have the edge to win Republican-held seats.

CQ Politics also has applied a rating of “Leans Democrat” to the Senate race in New Mexico, where Democratic Rep. Tom Udall , a cousin of Mark Udall , presently is favored against Republican Rep. Steve Pearce for the seat of retiring Republican Sen. Pete V. Domenici .

CQ Politics has long rated the Virginia seat as the most likely to change party hands among the 35 on this year’s ballots. Democrat Mark Warner, a former governor, has a strong edge over Republican James S. Gilmore III, another former governor, for the seat of retiring Republican Sen. John W. Warner . The Virginia Senate race is rated “Democrat Favored,” meaning that Warner has a decisive advantage but that an upset by Gilmore cannot be completely ruled out.