An advertising blitz without real grass-roots support can go only so far with seasoned politicians.

“I always want to hear from my constituents,” Ms. Collins told reporters on Wednesday after an unrelated event in Orono, Maine. “What is not effective is when these advocacy groups spend millions of dollars on attack ads jamming my phone lines with out-of-state callers.”

Even Washington organizers concede things will need to pick up.

“We have a ways to go in terms of achieving the level of mobilization that we need to see,” said Brian Fallon, the executive director of Demand Justice, a group that promotes progressive judicial nominees, even as he argued that there was a path to defeating Judge Kavanaugh’s nomination.

Mr. Fallon and others are hoping that an August blitz centered on the Senate’s nearly two-week recess can provide a jolt. Larger national advocacy groups — including Planned Parenthood Action Fund and Protect Our Care — told reporters on Monday that they had more than 100 “actions” planned in key states, from letter writing and phone banks to rallies.

In Alaska, voters have been inundated with broadcast and online advertisements targeting Senator Lisa Murkowski, a Republican who, like Ms. Collins, supports abortion rights. And in Nevada, Dean Heller, the most endangered Republican senator up for re-election, has faced a similar barrage.

In Portland, Maine, activists streamed into Ms. Collins’s office each day this past week, sharing with her staff vivid stories of abortions and health crises, iPhone cameras rolling in hand. Signs plastered onto lamp posts and walls around the city asked voters to call Ms. Collins and demand a “no” vote. Labor organizers paused on Thursday during an annual summer teach-in in Orono, not far from Ms. Collins’s home in Bangor, so attendees could call the senator’s office.

“Rise Up for Roe,” a nationwide tour organized by Demand Justice, was scheduled to stop in the city on Sunday.