Polls have shown that voters are willing to separate their support for certain House and Senate candidates from their feelings about the top of the ticket. In an effort to bolster Ms. Comstock and other vulnerable Republicans, the Congressional Leadership Fund, a “super PAC” aligned with Republicans, announced Friday that it would invest an additional $10 million into 15 targeted races, including hers.

Speaker Paul D. Ryan of Wisconsin also has tried to ensure his party holds its House majority, offering a policy agenda and promising appearances in dozens of cities to lend his fund-raising power.

His campaign said on Thursday that Mr. Ryan had raised $15.4 million in the third quarter, collecting more than $48.2 million in 2016. He has transferred more than $31 million of that to the National Republican Congressional Campaign Committee.

Mr. Ryan — having disinvited Mr. Trump from their first planned joint appearance in Wisconsin last weekend after news of the recording broke — effectively cut his members free on Monday, saying he would not defend nor campaign with Mr. Trump. He has instead shifted his focus to the argument that Republicans need to be re-elected to serve as a bulwark against a potential President Hillary Clinton.

Representative Nancy Pelosi of California, the Democratic leader, has proved once more to be a fund-raising powerhouse, raising $34.6 million for House Democrats in the third quarter and $127.7 million this election cycle, the Democratic Congressional Campaign Committee said on Wednesday.