AURORA, Colo. — As the weather warms, Lizeth Chacon is anticipating a new season of registering Latino voters — yet dreading experiences like one late last year, when she came upon a skate park full of older teenagers.

“I thought, ‘The perfect age! They’re turning 18,’ ” said Ms. Chacon, just 26 herself, born in Mexico and now the lead organizer at Rights for All People, a local immigrant organizing group. But among the roughly 50 people she approached in this increasingly diverse city east of Denver, “not a single person” was interested in her pitch, including those already old enough to vote: “They were like, ‘Why? Why would I bother to vote?’ ”

Across the country, immigrant-rights advocates report mounting disillusionment with both parties among Latinos, enough to threaten recent gains in voting participation that have reshaped politics to Democrats’ advantage nationally, and in states like Colorado with significant Latino populations. High hopes — kindled by President Obama’s elections and stoked in June by Senate passage of the most significant overhaul of immigration law in a generation, with a path to citizenship for about 11 million people here unlawfully — have been all but dashed.

Latinos mainly blame Republicans, who control the House and have buried the Senate bill, but they also have soured on Mr. Obama. The federal government has so aggressively enforced existing immigration laws that one national Hispanic leader recently nicknamed the president “deporter in chief” for allowing nearly two million people to be deported.