Heckled by his own party's millionaire donor: Mark Udall campaign hit by friendly fire Colorado's senior Democratic senator was reaching the climax of his stump speech when one of his party's millionaire donors started to heckle him. Mark Udall had been looking confident, just moments earlier, when he climbed down the steps of his campaign bus and began addressing what should have been an audience of the party faithful. These were people who had given up their Sunday afternoon to knock on doors in Centennial, in the southern suburbs of Denver, in search of votes for Udall. In a populist, energising speech, Udall mocked the "plutocrat" Koch brothers, who bankrolled TV ads for his Republican rival Cory Gardner, and praised "the clipboard army" who were about to begin knocking on doors. I know you can do it. We're surging. Ignore the polls. The crowd cheered and autumn leaves fluttered about the senator like confetti. Then, finally, came the only reference to policy in Udall's speech. "And by the way, I'm proud to stand with Colorado's women," he said, almost as an aside. I'm proud to stand for reproductive freedom. An angry voice from the crowd jeered: "That's not the only thing you stand for! Jesus Christ! Udall turned to a short, dark man on his left. The senator look genuinely stunned. I'm sorry? That's not the only thing you stand for! The heckler was Leo Beserra, a 73-year-old who made millions on Wall Street and, since the early 1990s, has shared a generous slice of that wealth with Colorado Democrats. Beserra's grievance - that the senator's narrow focus on abortion has backfired - is shared by others in the party, but rarely voiced in public and never in the middle of the candidate's campaign speech. Udall is not the only Democratic candidate to campaign hard on his opponent's position on women's issues; Democrats in several key Senate races, including Iowa, have tried to paint their Republican adversaries as the protagonists in a war on women. It is a playbook that resonated in 2012, when Republicans fielded a slew of more conservative candidates, including Todd Akin, whose remarks about "legitimate rape" lost him the Senate race in Missouri and tarnished his party's wider reputation. But this year, the mud just hasn't stuck. Udall's attempts to frame the Colorado race as a battle over women's rights have been particularly relentless and, seemingly, ineffective. The senator's supporters contend that his attacks against Gardner have been justified. As a congressman, Gardner co-sponsored a federal "personhood" bill that extends citizenship rights to embryos. He has since shifted position, side-stepping his own record and endorsing a policy of over-the-counter contraception. But others complain that Udall's campaign has been dull, uninspiring and one-dimensional, earning him the moniker "Senator Uterus." His naysayers even include the left-leaning Denver Post, which ended up endorsing Gardner. "Udall is trying to frighten voters rather than inspire them with a hopeful vision," Colorado's biggest newspaper concluded in its editorial earlier this month. His obnoxious one-issue campaign is an insult to those he seeks to convince. And, as Beserra revealed, Udall's critics also include some in his own party. Seeking to downplay Beserra's disagreement with the senator, Democratic party staffers said the donor is an eccentric, sometimes outspoken figure. That may be true. But he is an undeniably important Democrat in Colorado; campaign finance records reveal that he has spent $10,100 on Democratic candidates and liberal political action committees this cycle alone. He has not donated directly to Udall's campaign this cycle, though he did contribute to Udall's initial run for the Senate in 2008. And he comes from an esteemed Democratic Hispanic family. His uncle, the late Ed Roybal, was a Democratic congressman in California for three decades; his cousin, Lucille Roybal-Allard, has been a congresswoman in the same state since 1993. Perhaps more importantly, Beserra had given up his Sunday afternoon to persuade voters to back Udall. Minutes after interrupting the senator's speech, he vented, once again, to the Guardian. I'm trying to figure out who in the hell decided this was how the campaign was supposed to go. He said he had just watched a Sunday morning talkshow in which Udall was ridiculed. Who is running the worst campaign? Him. Because fucking abortion is all he talks about. He should not talk about it any more whatsoever. There are so many other issues. Referring to the 2012 election strategy, Beserra added: "Two years ago it might have made sense. But didn't they get an inkling that it wasn't working [this year]? Later in the day, outside a field office in Lakewood, in the western suburbs of the city, Udall told the Guardian that the criticism Beserra levelled at him was unfounded. He said his campaign had emphasised the issue of reproductive rights because it illustrates Gardner's deeply conservative leanings on a host of other issues. "This is emblematic, for me, of his extreme positions," he said. I've said reproductive freedom is important to millions of Coloradans and their families. The important thing to remember is that Congressman Gardner's focus on limiting those reproductive freedoms is an indication of his extreme position on everything from climate change to affordable college tuition, to protecting social security and Medicare. I'm running on my record; it is a mainstream record. He is running away from his record, which is an extreme record," he added. My sense right now is that it finally has resonated: that's why we're going to win this race. Experts believe it is, indeed, possible for Udall to emerge victorious on Tuesday, but the signs are not good for the incumbent senator. Polls suggest Gardner opened up a lead over Udall over the course of the campaign, although that advantage may have narrowed in the final stretch of the race. A poll released on Monday by Quinnipiac University had Gardner at 45% and Udall at 43% - well within the survey's margin of error. Udall's team argue that any edge Gardner may enjoy in surveys will be countered by the Democratic party's get-out-the-vote machine, which is notoriously effective in Colorado. Yet the turnout evidence so far has been disappointing for Democrats. Early ballot returns in Colorado's first major mail-in election have favoured Republicans, who by Friday had cast 104,000 more ballots in the state than Democrats. It is not unusual for Republicans to lead in early ballot returns, but the scale of their advantage has surprised political analysts. The lead is not unassailable, and there were signs over the weekend that a late surge of younger voters and registered Democrats has begun to narrow the gap. But it is an uphill battle for Udall and other Democrats in Colorado. Others who may be concerned are the state's incumbent governor, John Hickenlooper, who is in a tight re-election race, and Andrew Romanoff, who is seeking to dislodge the sitting Republican congressman, Mike Coffman, in the highly competitive sixth congressional district. Romanoff told the Guardian his party was putting all its efforts into reaching the 200,000 voters who had yet to return their ballots. He sought to put a positive spin on the advantage Republicans have so far notched up in Colorado's ballot count. "Sure, more Republicans than Democrats have voted," he said. But that means there are more Democrats than Republicans who can still vote. This article was updated on 3 November 2014 to clarify that Leo Beserra donated to Senator Mark Udall's election campaign in 2008. In this cycle he has donated to Democractic causes but not to the sentator's re-election bid.