While talk of Rep. Mark Udall’s (D-Colo.) replacement has centered around state Senate President Joan Fitz-Gerald (D) and millionaire Jared Polis (D), either could be overtaken in a Democratic primary by a candidate who better fits the liberal 2nd district — should such an individual choose to run.

Udall is presumably vacating the seat next year to run for Senate, and either Fitz-Gerald or Polis is a fine political fit for the seat, most Democrats agree. But neither offers the mix of liberal politics and Mountain West temperament that has made Udall an institution, leaving an opportunity for another candidate to exploit this opening and steal the Democratic nomination away from the frontrunners, some party insiders say.

“There’s an opening for the right person. It remains to be seen if anyone will try and fill it,” said one Colorado Democrat with knowledge of the suburban Denver district.

Udall’s decision to run for Senate next year has left an already heated primary contest to succeed him in its wake between Fitz-Gerald and Polis. The winner of the August Democratic primary almost assuredly will win the general election and advance to Congress, as Sen. John Kerry (D-Mass.) beat President Bush in the 2nd district in the 2004 presidential race by 17 points.

Fitz-Gerald and Polis jumped into the race early. Each is formidable and has connections to Democratic grass-roots activists. Fitz-Gerald is a dogged campaigner and prolific fundraiser, while Polis is personally wealthy and has a history of community service and philanthropy.

But each candidate has a political downside, which is why the names of other potential Democratic contenders are percolating, including environmental activist Will Shafroth; Adams County District Attorney Don Quick; and state Sen. Ron Tupa (D). Quick has ties to Sen. Ken Salazar (D-Colo.) and Gov. Bill Ritter (D), while Shafroth has strong support among Colorado’s environmental activist community and hails from a family with a strong political pedigree.

Democrats Bill Hunt and Larry Johnson, who are both attorneys, also are considering jumping into the race.

Colorado Democrats caution against underestimating Fitz-Gerald, who has been the chief fundraiser for state Senate Democrats at home and the Democratic Legislative Campaign Committee nationally. She also would appear to be in line to receive an endorsement from EMILY’s List, which could further swell her campaign coffers.

But Fitz-Gerald is not native to the district — she was born in New York City — and does not reflect the rugged, independent-minded Mountain West disposition that Udall exhibits and that reflects a significant portion of the district’s electorate.

Polis, a wealthy Internet and media entrepreneur who is still in his 30s, has served on the state Board of Education and has plenty of his own money to compete with Fitz-Gerald’s fundraising prowess. But he too lacks Udall’s unique profile of liberal politician as outdoorsman.

Additionally, Polis has to overcome the notion that he is trying to use his money to buy a House seat — a charge that hampered his Board of Education campaigns — not to mention the political trouble he created for himself by championing Amendment 41, a ballot initiative intended as a reform measure to get lobbyists out of state politics.

Amendment 41 was passed by the voters in November but has angered many Democratic Party insiders and activists because it was drafted in a way that could be defined so broadly that it might, for instance, exclude the children of state employees from being eligible for college scholarships. Fitz-Gerald has been among the leading critics of the measure.

Accordingly, some Colorado Democrats say a race that is currently dominated by Fitz-Gerald and Polis could end up attracting another candidate — or candidates — by the time primary voters go to the polls.

“I think there is plenty of time for one or two or more candidates to get into this thing,” said one Democratic operative based in Colorado.

Democrats have experienced increasing success in Colorado over the past few cycles. Bush won the state in 2004, but in that same election Salazar defeated beer magnate Pete Coors (R) to score a Senate seat for Democrats, while Salazar’s brother, now-Rep. John Salazar (D), won the 3rd district seat held for six terms by former Rep. Scott McInnis (R).

Democrats also made gains at the state level, taking over both chambers of the Legislature in 2004 and winning the governorship in 2006.

Colorado Democratic Party Chairwoman Pat Waak said Democrats should have no trouble holding the 2nd district, regardless of who emerges from the Democratic primary. Though initially a competitive seat — Udall won it with just 50 percent of the vote in his first race in 1998 — it has trended increasingly Democratic, with the incumbent securing 55 percent of the vote in 2000, 60 percent in 2002, and 67 percent in both 2004 and 2006.

“We have some great candidates running, all with great Democratic credentials, and all would serve us well in the U.S. Congress,” Waak said.

For Democrats in Colorado, obtaining a position on the ballot is more involved than filling out paperwork and paying a fee, which is why there may not be a crowded free-for-all primary.

To get on the ballot, a prospective Congressional candidate has to secure the support of 30 percent of caucusgoers at the Democratic Party caucus for the House district in question. Absent that, prospective candidates can petition their way onto the ballot by obtaining the valid signatures of 1,000 registered Democrat who live in the Congressional district.

Udall petitioned his way onto the ballot in 1998 and went on to win the general election. In last year’s Democratic primary for the 7th district, now-Rep. Ed Perlmutter (D) advanced to the ballot by winning the caucus. Former state Rep. Peggy Lamm, whom Perlmutter defeated in the Democratic primary, petitioned onto the ballot.