With a rapidly growing Hispanic population back home, Mr. Reid had ample incentive to try to increase his appeal to that constituency and organize Hispanics politically even when others advised against it or saw it as fruitless.

“People immediately started making fun of me in their own way,” he said. ‘Why are you wasting your time? No. 1, most of them are illegal. And even if you get some to register, they never vote.’ ”

As he made inroads, Mr. Reid said he reminded Hispanics that the only way to gain political power was to vote. Through his efforts to encourage greater political participation, Mr. Reid said he developed deeper personal ties and a new affinity for the community as he regularly attended local festivals and Christmas and Cinco de Mayo celebrations.

“They were kind of fun,” he said of the events. “They had music and food and people were happy.”

When it came to the music, Mr. Reid saw a way to help. Never one to shy away from pushing an earmark through the Appropriations Committee, Mr. Reid in 2004 secured a $25,000 grant for Clark County schools in Las Vegas to begin a mariachi program. The federal spending was ridiculed by Citizens Against Government Waste as “La Pork-a-Racha,” but it was immensely popular with Hispanic students and their parents.

“That is one of the best things I have ever done in my political life,” said Mr. Reid, who still cannot help smiling about the earmark.

For Mr. Reid, the true test of growing Hispanic political might in Nevada came in 2010, when he was deemed to be in jeopardy of losing his seat.

With Nevada among the states with the highest concentration of unauthorized immigrants, Mr. Reid’s opponent, Sharron Angle, a Tea Party favorite, moved aggressively to undercut Mr. Reid on his immigration stance with ads and mailers that described him as “the best friend an illegal alien ever had.”