WASHINGTON — House Republicans are united as ever in their election-year opposition to “Obamacare,” but they’re increasingly divided over their promise to vote this year on an alternative to it.

The disagreement comes amid a shifting political calculus around President Barack Obama’s health care law. Millions are enrolled for medical insurance through the law’s exchanges, and an all-out repeal has become less practical and popular. Some Democrats have begun promoting the measure in campaign commercials, and some Republicans are treading more carefully in belittling the program.

At a recent closed-door House Republican caucus meeting, several conservatives pressed GOP leaders over the pledge Majority Leader Eric Cantor made in January that House Republicans would rally around an alternative to “Obamacare” and pass it this year.

“We said at the retreat in January we were going to do this. Well it’s June and we still haven’t done it,” Rep. Phil Roe, R-Tenn., said he told Cantor during the meeting last week. “It’s moving at a snail’s pace. … We want to be for something.”

Roe said he got little reply beyond polite attention. Cantor’s spokesman, Doug Heye, said, “Majority Leader Cantor continues to work towards bold legislative solutions to replace ‘Obamacare.’”