Despite not serving in or running for the United States Senate, House Minority Leader Nancy Pelosi is becoming the favorite foil in Republican Senate races.

"In Congress, [Nevada Democratic Senate candidate] Jacky Rosen voted with Pelosi nearly 90 percent of time," said the narrator in a Republican ad on the air in Nevada, which mirrors the national trend of attacking Pelosi in the country's most competitive Senate races – despite her not serving in or running for a seat in the Senate.

"Pelosi to give amnesty to millions of illegal immigrants," claims an ad tying West Virginia Sen. Joe Manchin to Pelosi. Sen. Claire McCaskill's race in Missouri ties her to Pelosi through an unpopular tax plan.

The ads are paid for by the Senate Leadership Fund, which is co-founded by Bush-era political guru and Fox News contributor Karl Rove.

"There is a huge visceral reaction to her," Rove said. "So she's got a higher profile than say [New York Sen.] Chuck Schumer. She's seen as more active and more in the center of things than [former Vice President] Joe Biden and she is certainly far less popular than somebody say like Barack or Michelle Obama."

In Fox News national poll shows just 29 percent of registered voters have a favorable opinion of Pelosi, a fact exploited by President Trump at his rallies for Republican Senate candidates. At a September rally in Missouri, he said, "A vote for Claire McCaskill is a vote for Nancy Pelosi."

In Montana, he said: "[Sen.] Jon Tester talks like he's from Montana, but he votes like he's Nancy Pelosi."

Despite seemingly negative portrayals of Pelosi by Republicans – images like her as then-House speaker passing Obamacare – she remains a fundraising machine among Democrats. In the third quarter, she held 250 fundraising events in 29 cities, raising $34.2 million for Democrats for a total of $121.7 million this election cycle.

Democrats give money when Pelosi asks because she has delivered for Democrats on issues that are top concerns for not just Democrats, but other Americans across the board, said Jehmu Greene, a former Democratic National Committee chairwoman candidate.

Since her rise to leadership in 2002, Pelosi has raised more than half a billion dollars for Democrats. Now, many wonder if all that cash is worth the political cost.

In at least 46 house races, Democratic candidates have already said they won’t vote for her for House speaker.