In the basement of a northwest Denver office building, blue "Latinos con Udall" signs adorned the wall behind Arturo Rodriguez as he pressed the need for immigration reform and appealed to the crowd in the small room.

"Those of us who are Latinos, we know we’re family-oriented," said Rodriquez, the national president of the United Farmworkers of America, as he stood next to Sen. Mark Udall. "So we’ve got to becien por ciento — we’ve got to be 100 percent — in ensuring that all of our family votes."

For Udall, that Latino turnout could make all the difference in a tight race against Republican challenger, U.S. Rep. Cory Gardner. Also at stake, potentially, is Democrats’ control of the U.S. Senate.

Two years ago, Latinos were 14 percent of voters when President Barack Obama won Colorado. They also helped Sen. Michael Bennet eke out a 2010 victory."The Hispanic vote is ultimately what Mark Udall’s hopes rest on," said Kevin Ingham at Strategies 360, a Denver political consulting firm that focused on Latino voters in a survey released Wednesday. "If they do not turn out, then the race is going to end up going to Gardner."

The question this year is whether Latino voters, disenchanted after years of inaction on immigration reform, will continue to boost Democrats to victory.

National and state polls suggest Latino citizens may not be as motivated to vote this year.

Udall is hoping to convince them to not lose hope. Flanked by Latino leaders and a seven-piece mariachi band in Denver, the incumbent Democrat made several stops Saturday in Latino strongholds to fire up volunteers and supporters.

Republicans are making it harder this year, offering more appeals than usual to Latino voters. Gardner debuted a Spanish-language TV ad and attended a Hispanic business event Wednesday with former Florida Gov. Jeb Bush in Denver.

Democrats see the growing base of Latino voters as a key to winning Udall’s and other tight races Tuesday, including the one between Gov. John Hickenlooper and Republican Bob Beauprez as well as a suburban Denver congressional race.

Underlining the importance of the Latino vote, the candidates in the 6th Congressional District will participate in the Colorado’s first-ever debate in Spanish on Thursday. U.S. Rep. Mike Coffman, a Republican who has been learning Spanish with a tutor, and Democrat Andrew Romanoff, who is fluent, will meet for 30 minutes at 5 p.m. for a live exchange on the Denver Univision affiliate.

They are vying to represent the highly competitive — and heavily Latino — 6th Congressional District, centered in Aurora.

Unlike in typical debates, the station agreed to Coffman’s request to provide questions in advance so that the candidates could prepare answers.

Disagreement over immigration reform

In that race, the three-term incumbent rapidly has adapted his views on immigration to remain competitive following redistricting, supporting a path to legal status for immigrants in the country illegally — but not citizenship. Romanoff has argued that Coffman’s preferred reforms don’t go far enough.

At the top of the ballot, immigration is not dominating the conversation.

Earlier this year, Udall pushed the White House to take executive action on immigration while the Republican-controlled House refused to act on a far-reaching bipartisan Senate bill he supported that included a path to citizenship.

Gardner has softened his stance on immigration to separate himself from his party’s hard-liners, focusing on the need for border security and an undefined "earned status" for immigrants that likely includes paying back taxes.

In the governor’s race, Hickenlooper and Beauprez have disagreed prominently on a Democrat-authored program to allow driver’s licenses for immigrants in the country illegally.

Robert R. Preuhs, who researches the influence of racial and ethnic politics, said Colorado’s high-profile campaigns mostly have focused on other issues, including women’s reproductive rights, giving Latino issues less prominence.

"What’s surprised me in terms of Latino voters is the fundamental absence of immigration reform among the Democrats," said Preuhs, an associate professor of political science at Metro State University in Denver.

The immigration debate, though, has influenced how many Latinos view the candidates, even if Republicans try to blame Democrats in Congress for contributing to the stalemate on the issue.

More recently, President Barack Obama has put off the chance of using executive orders to enact some reform until after the election, denying Democrats such as Udall a tangible win he can tout.

Anita Duran, 74, a retiree who is a Latino outreach volunteer for Romanoff’s campaign, says immigration is the top issue she hears from potential voters — along with frustration over the topic.

"To a certain point, they are frustrated," Duran said in Spanish during a recent campaign stop in Aurora. "Some understand a little bit that many times, even though the president wants to do some things, he doesn’t have the support of the Republicans — which is what is failing us right now."

But pollsters, political experts and community leaders say Latinos also are focused on the same issues that capture other voters’ attention: the economy, the need for more good-paying jobs, educational opportunity and health care.

But gauging which candidates they support has been difficult, with Democrats and pollsters arguing that many public polls showing Gardner with a lead in the Senate race undercount Latino voters and skews the results.

A Strategies 360 poll this week that included a strong sample of likely Latino voters showed Udall and Gardner in a statistical tie. But among likely Latino voters, Udall was winning 58 percent to 26 percent. The poll included a larger sample of Latinos than is typical, but they were weighted in the overall poll to represent 10 percent of expected turnout.

Republicans recognize need for outreach

But far from a monolith, Colorado’s Latinos have a longer history of settlement here than in some states. Some families go back six generations or longer, while others arrived in the United States and Colorado more recently, with varying legal status.

State Sen. George Rivera, a Pueblo Republican, was born a citizen but recalled that his mother and siblings returned to Mexico decades ago to start the citizenship process. Similar experiences leave some Latinos resentful, he said, of recent immigrants’ pleas for a faster path to citizenship.

Still, said Marco Reyna, a 51-year-old Aurora construction worker, Democrats "care more about us — that’s why I vote for them." He said he turned in his ballot last week.

Similarly disaffected by the GOP is Damian Alcazar, 43, a truck driver who also lives in Aurora. Though he once favored Republicans and still is registered as one, last week he was at a rally for Udall and other Democrats that was led by former President Bill Clinton, and he said he’d been volunteering for Democratic campaigns.

"As I hear the rhetoric coming from Republicans, I cannot support it," Alcazar said, referring in part to how some conservative hard-liners have talked about immigrants from his native Mexico. "They make it sound like an invasion."

Maria Garcia Berry, a prominent Denver Republican who serves as finance chair for Gardner’s campaign, is used to getting frequent push-back from other Latinos for similar reasons.

"I think we absolutely have to solve that perception," she said, by working more constructively on immigration and other issues.

But she also has a pitch for why Latinos should give the GOP a chance: "You know what, if I don’t stay in the Republican Party and continue to work on some of these issues I care about, the other people who don’t think like me get more of a say."

Key Republican strategists admit the party made little concerted effort to appeal to Colorado Latinos in recent elections. For the past 18 months, they’ve been taking what they see as a long-term approach — financed by the state party and the Republican National Committee — that may not pay sizeable dividends this year.

"The way you measure success is by the presence you have in the community," said Ali Pardo, the RNC’s Hispanic press secretary, who’s spent October working in Colorado. "You have to make sure that voters are listening to you, and after Election Day, they know that the Republican Party is not going away."

But aside from whom they’ll support, the main question this year is whether Latino voters are motivated to cast ballots, said Fernando Sergio, who hosts a Spanish-language radio show on KBNO (1280 AM). He supports Udall and Hickenlooper.

"Certainly the enthusiasm that was generated two years ago is not there," he said, referring to Obama’s 2012 win in Colorado.

But he said the palpable disappointment at Obama and the Democrats for failing to deliver on promises for immigration reform is being overridden by an increasing "fear" about what Republican wins would mean in Washington and Colorado.

"The question is whether you are going to stay home and let this happen," he said, "or are you going to do something about it?"

Jon Murray: 303-954-1405, jmurray@denverpost.com or twitter.com/JonMurray

Staff writers Lynn Bartels and Zahira Torres contributed to this article.