The Senate race in Colorado will enter a new and competitive phase today, when first-round precinct caucuses across the state unofficially kick off the campaign and serve as an early barometer of the candidates’ organizational strength and their support among base voters.

While Colorado’s caucus process — a multilayered procedure that will culminate at the state conventions on May 22 — isn’t necessarily predictive of success in the August primary election, it will give political activists their first real opportunity to weigh in on the competitive primaries for the seat Sen. Michael Bennet (D) is defending after his appointment 14 months ago. The leading vote-getters at the conventions earn top billing on the primary ballot.

“It is kind of the unofficial official start of the campaign season, if you will,” said Nate Strauch, a spokesman for former Lt. Gov. Jane Norton, the leading Republican in the race.

One candidate who needs a strong showing is former state Speaker Andrew Romanoff (D), who is challenging Bennet in the August primary. Romanoff wanted the Senate appointment that Gov. Bill Ritter (D) instead awarded to Bennet after Sen. Ken Salazar (D) resigned to join the Obama administration as Interior secretary.

Political analysts said Romanoff, who badly trails Bennet in fundraising, needs to perform very well at the caucuses to gain traction for the difficult undertaking of unseating a Senator in a primary.

“My current assumption is that Romanoff needs to win … to credibly make the argument that ‘I’m the grass-roots guy,” independent Colorado pollster Floyd Ciruli said.

Eric Sondermann, an independent political analyst in Denver, described the caucuses as “a home game for Andrew Romanoff” because he’s concentrating on securing the support of the sliver of Democrats who will participate. He expects Romanoff to do well.

“If he does not fare well [today] in the caucuses, it’s hard to understand what the ongoing rationale for his candidacy is,” Sondermann said.

Katy Atkinson, a Denver-based political consultant, said the caucuses are far less important for Bennet than for Romanoff because “Bennet has the money to be able to run a primary campaign, and Romanoff needs the momentum that a convention win would give him to help him raise more money.”

Bennet’s campaign is targeting the caucuses to build the full-fledged statewide political organization he lacked after coming to the Senate as an unelected Member with no experience in elective office.

“The caucuses have been great for him to go around and do retail politics, meeting voters in smaller settings, listening to their concerns and building up a grass-roots organizations, which is what we’ve used the caucuses to do,” said Craig Hughes, Bennet’s campaign manager.

The Senator has been burnishing his public image in recent months. He’s been a vigorous supporter of a public health insurance option and recently unveiled an ethics proposal that includes banning Members of Congress from becoming lobbyists and changing rules governing earmarks and Senate filibusters.

With little to distinguish him from Bennet on policy — “they’re both sort of policy-wonky moderate Democrats,” Ciruli said — Romanoff is trying to draw a distinction between how he and Bennet are raising their money. Unlike Bennet, Romanoff is forswearing contributions from political action committees on the grounds that such funds have a corrupting influence.

“The message is changing Washington. Corporate cash that’s corrupting the system — he’s been hammering that theme pretty hard,” said Dean Toda, a spokesman for Romanoff’s campaign.

Hughes said Bennet is an “independent voice for Colorado” who has taken votes at odds with the positions of some of his donors. His campaign has also noted that Romanoff accepted PAC money when he was a Colorado legislator.

Romanoff’s campaign also says he is the more electable Democrat, pointing to polls that show him running more strongly than Bennet against Norton. Hughes said the Bennet campaign is comfortable with the current polling, given the difficult political environment for incumbents.

A survey taken March 5-8 by Public Policy Polling had Bennet ahead of Romanoff in a hypothetical primary, 40 percent to 34 percent, with 26 percent of likely Democratic voters undecided.

On the Republican side, Norton enters the caucuses as the Republican frontrunner. She’s armed with endorsements from GOP luminaries in Washington, D.C., and Colorado — including many Senators — and is targeting caucus-goers with an aggressive media campaign that includes two television ads and two radio ads.

Some party activists aren’t convinced of her conservative bona fides and don’t like that party establishment figures are backing her.

Her best-funded opponent is Tom Wiens, a businessman, rancher and former state Senator who is running to Norton’s right. He’s been emphasizing a record of fiscal conservatism, including his opposition to a 2005 referendum that relaxed limits on the amount of revenue that the state could capture each fiscal year. Norton supported the measure, which Wiens’ campaign says is tantamount to having “supported the largest tax increase in Colorado history.”

“I think it’s really important that voters know that she’s not exactly the fiscal conservative she claims to be,” said Brandon Moody, Wiens’ campaign manager.

Strauch said that Norton was part of a gubernatorial administration that cut taxes 43 times and that the 2005 referendum was preferred by the voters.

Wiens has put more than $640,000 of his own money into the race and is the only one of Norton’s primary opponents who can compete with her financially.

Democratic officials, including the Democratic Senatorial Campaign Committee, have trained their fire on Norton, who polls the best among the Republican candidates. They’ve attacked a string of statements that they say put her outside the political mainstream — including her recent statement that the Social Security system “has turned into a Ponzi scheme.”

Strauch defended Norton’s description, saying that Social Security is “using new investors to pay off old investors” until the system runs out of money. “That’s what she was saying,” he said.

The third major Republican candidate is Ken Buck, a county district attorney who has raised little money but is a favorite of the tea party activists whose energy Buck hopes to parlay into a good showing at the caucuses.

The PPP poll had Norton ahead with 34 percent of the vote to 17 percent for Buck and 7 percent for Wiens.