WASHINGTON — Senate Republican leaders, facing their restive colleagues after the Fourth of July recess, vowed on Tuesday to press ahead with their effort to repeal and replace the Affordable Care Act, with a new version of their bill on Thursday and a vote next week — regardless of the deep divisions in the party.

The weeklong recess only seemed to generate more doubts about the Senate bill, but Senator Mitch McConnell of Kentucky, the majority leader, signaled that he was not ready to give up on his party’s seven-year-old promise to gut President Barack Obama’s signature domestic achievement. Accusing Democrats of obstructionism, he announced he would delay the Senate’s scheduled August recess by two weeks so that senators could keep working.

But pessimism among Republicans still pervaded the Capitol on Tuesday after a week in their home states that did little to resolve the disputes that thwarted a vote last month.

Senator Charles E. Grassley, Republican of Iowa, said Tuesday that he was “very pessimistic” about passing a bill, while Senator John McCain, Republican of Arizona, said it was “very possible, very probable” that the Senate bill was dead.