“I have indicated, gosh, at least for six weeks now, we are going to deal with the Lynch nomination right after we finish trafficking,” Mr. McConnell said on the floor Thursday.

Just the fact that Mr. McConnell, by his own admission, has been talking about it for at least six weeks is galling to Democrats, who think she should have been confirmed months ago. They see the Lynch nomination as a prime case of Republican partisan mischief and ill-treatment of woman with a distinguished career as a prosecutor.

While some difficulties were always expected with Ms. Lynch given the traditional political sensitivities of the post of attorney general, no one anticipated after her nomination on Nov. 8 that a vote would still be pending in late April.

As the United States attorney for the Eastern District of New York, Ms. Lynch had a formidable reputation as a prosecutor and administrator and had the strong backing of law enforcement and civil rights groups. Some of the most conservative Republicans were expected to oppose her, but her ultimate approval never seemed in doubt.

But at her confirmation hearing on Jan. 28, Ms. Lynch said she found it reasonable that the Justice Department had concluded that Mr. Obama was acting within the limits of his power when he decided to unilaterally ease the threat of deportation against millions of undocumented immigrants. That quickly cost her backing among Republicans who said they could not vote for Ms. Lynch if she was willing to side with the president on his immigration actions.