In the Senate race in Colorado, for example, where Latinos make up 14 percent of voters, a conservative Republican, Cory Gardner, took the seat of the incumbent Democrat, Mark Udall, in what analysts from both parties called a Republican playbook on how to blunt the Democrats’ advantage with Hispanics. Mr. Gardner generally avoided the contentious issue of immigration but campaigned in Latino neighborhoods with a message of job creation and smaller government…

“It was a real miscalculation by the Udall campaign not to make immigration reform and the lack of movement on that issue part of his campaign,” said Arturo Vargas, executive director of the National Association of Latino Elected and Appointed Officials, a bipartisan organization. In an election eve poll by Latino Decisions, a research group, a plurality of 45 percent of Latino voters nationwide said immigration was the most important issue for their communities that politicians should address.

Latino strategists and Democrats said the results would place new pressure on President Obama to take broad executive action to give protection from deportation for immigrants in the country illegally. At a White House news conference on Wednesday, Mr. Obama repeated his intention to unveil those measures before the end of the year. Earlier in the fall, he postponed his announcement, responding to the fears of endangered Democrats in Senate races that it could thrust a toxic issue into their campaigns.