If Colorado’s Democratic US Senate primary were simply a contest between former Assembly Speaker Andrew Romanoff, a savvy activist and organizer who has played a leading role in the remarkable renewal of the state party’s fortunes, and Michael Bennet, former managing director of an investment firm whose tenure as superintendent of the Denver public schools stirred so much resentment from teachers that their union is leading the charge for Romanoff, it wouldn’t be much of a contest. There are few scenarios where Romanoff, a progressive with honors from Governing magazine as a 2008 "Public Official of the Year," would have much trouble beating Bennet, who grew up in a politically connected Washington family and is mounting his first campaign in Colorado.

The August 10 primary is no simple contest, however. When Senator Ken Salazar became interior secretary, Governor Bill Ritter quickly tapped Bennet to replace him. Bennet now runs with the trappings of incumbency: a campaign treasury overflowing with special-interest money and a warm endorsement from Barack Obama. For a time, it seemed that would be enough to secure Bennet the Democratic nod in a year when national party strategists want to protect incumbents, and local Democrats fret that their recent winning streak—they control the governorship, both Senate seats, a majority of House seats and the legislature in a state that backed George Bush in 2000 and 2004—might be tough to maintain. Romanoff faced pressure to avoid forcing a primary; there were hints about Obama administration job offers similar to those Pennsylvania Congressman Joe Sestak said were made to prevent him from mounting the challenge that displaced Obama-backed Senator Arlen Specter.

But Romanoff went for it, launching an unapologetically populist campaign decrying "sabotage" not only by "Republicans who stand against us" but also "Democrats who sell us out." That’s not exactly a dig at Obama, but Romanoff is swinging hard at Bennet, whom the challenger accuses of taking corporate cash and then buckling on big issues such as Wall Street reform, with votes against amendments to break up "too big to fail" banks and protect homeowners from foreclosures. "The voters of Colorado face a fundamental choice," says Romanoff. "We get to decide whether to perpetuate a pay-to-play political culture that sells Senate seats to the highest bidder or to restore the role of people as the legitimate source of power." Bennet backers counter that he’s voted with Senate Democrats on major issues, and they accuse Romanoff of running a "scorched-earth" campaign. Romanoff—who refuses PAC money—has hit back by releasing detailed lists of contributions to Bennet from finance, insurance and pharmaceutical giants and the oil industry. In fairness to Bennet, some of that money comes from labor unions.

Bennet’s campaign argues that Obama’s backing and their man’s money advantage will see him to victory, and they may be right. If Bennet has the bucks and the TV-time advantage, however, Romanoff’s got the base; at the state Democratic Assembly in May, 60 percent of delegates backed him. Many of these hardcore party activists share the view of Bill Clinton, a Romanoff backer, who says the ex-legislator has "the best chance to hold this seat in November." There’s a general sense that Democratic prospects are looking up in Colorado, as the Republicans eat their own—the party’s gubernatorial contenders are plagued by so many scandals that former Congressman Tom Tancredo is preparing to mount a third-party campaign. A GOP Senate primary pits former Lieutenant Governor Jane Norton, the choice of DC strategists, against local prosecutor Ken Buck, a Tea Party favorite who says Republicans should back him because "I do not wear high heels." Even as the Republicans batter themselves—and, in Norton’s case, scare independents by expressing regard for Tancredo’s view that Obama poses "a more serious threat to America than Al Qaeda"—2010 could still be a hard year for Democrats who come off as Washington insiders. This is the point Romanoff keeps hitting home as he tells grassroots Democrats that his campaign’s message "to our own party is this: stiffen your spine or step out of the way."

That’s a resonant line. In a tough election year for Democrats, economic populists—especially those who gain nomination by taking on the national party establishment—are a lot more likely than centrist technocrats to defeat Tea Partisans. The same goes for the Senate, where there is nothing the Democratic caucus so requires as an infusion of progressives with legislative skills—and independent streaks that allow them to work with the president when possible but challenge him when necessary.