By ALAN FRAM, Associated Press

WASHINGTON (AP) — A new fundraising email from House Speaker Paul Ryan's political operation, over former Speaker Newt Gingrich's signature, seeks money for Republican congressional candidates by calling the appeal "our very last chance to stop Pelosi and Hillary."

Indiana Republican Trey Hollingsworth says in one TV ad that he's running for Congress to stop three Democrats — opponent Shelli Yoder, presidential candidate Hillary Clinton and House Speaker Nancy Pelosi — from imposing "higher taxes and government-run health care." In another spot, the GOP-aligned Senate Leadership Fund attacks the Democratic Senate challenger in Missouri by saying, "It's surprising how many ways Jason Kander is just like Hillary Clinton."

With polls showing Republican presidential candidate Donald Trump facing a steep path to victory, GOP candidates are increasingly seeking voters' support by saying they will check Clinton's agenda.

Some of the ads are being funded by a last-minute infusion of cash from the Senate Leadership Fund, a major super PAC focused on Senate races and run by allies of Senate Majority Leader Mitch McConnell. The group announced Tuesday it is spending $25 million for the final stretch in six key states: Indiana, New Hampshire, Nevada, Pennsylvania, North Carolina and Missouri.

The investment comes after public complaints from the Republican Party's Senate committee that it faced being outspent badly by Democrats in the election's final stretch. GOP outside groups are responding, including additional investments by the Chamber of Commerce.

Republicans hope that a loathing for Clinton will drive voters to the polls who otherwise might stay home because of their aversion to Trump.

Yet the value of the check-and-balance tactic is questioned by both parties' strategists as voters express fatigue with gridlock and a desire that Washington address problems like the slow-growing economy.

"The tightrope you walk is that assuming a Hillary win can potentially depress your base" voters' turnout, said GOP pollster Jon McHenry. But he said with Clinton's favorability ratings nearly as low as Trump's, arguing you will prevent Clinton from getting "free rein" in Washington is "a potent argument for a lot of independents."

The tactic is popping up in spots around the country, among them:

—A new ad by the American Action Network, which backs House Republicans, morphs a picture of Michigan Democratic House candidate Lon Johnson into Clinton and says both have "taken a fortune from special interests." Another by the network that starts Wednesday calls Suzanna Shkreli, a Democratic candidate in a second Michigan district, "a rubberstamp for Washington insiders" as pictures are shown of Clinton and Pelosi.

—In central California, the Congressional Leadership Fund supports GOP Rep. Jeff Denham by saying Democratic challenger Michael Eggman and Clinton back the dangerous nuclear arms pact with Iran, though "California families know they're wrong."

—The National Republican Congressional Committee, the House GOP campaign organization, says Democratic candidate Emily Cain "sides with Hillary, not with us" as she tries unseating freshman Republican Rep. Bruce Poliquin.

—An NRCC spot says first-term Rep. Brad Ashford, D-Neb., "says he's with us, but Clinton and Pelosi know he's with them."

—And west Texas GOP Rep. Will Hurd has an ad calling himself "the only candidate willing to stand up to Hillary Clinton and Donald Trump."

The reliance on the tactic comes with Republicans worried that a poor Trump showing could help Democrats capture a Senate majority and erode GOP House control.

The email from Ryan's political organization seeks contributions "to ensure the last line of defense for conservative values doesn't fall into the clutches of Hillary." After months of clashes, Ryan has refused to campaign for Trump and the presidential candidate has savaged the speaker on Twitter.

Asked why Ryan was adopting the check-and-balance approach, spokesman Zack Roday said Ryan "is focused on beating Democrats, including Hillary Clinton, on Election Day" and "committed to preserving our congressional majorities."

GOP pollster Robert Blizzard said the tactic works best if tied to issues Republican voters find emotional, like boosting taxes or expanding President Barack Obama's health care law. But he cautioned, "The easiest, most efficient, most effective way to defeat a Democratic candidate is to make that Democratic candidate unacceptable, unelectable."

Democrats say the tactic is flawed because it relies on two unlikely occurrences: Republicans repelled by Trump showing up to vote anyway, or people splitting their ticket between Clinton and a GOP congressional candidate.

"The national tide is running very strongly against down-ballot Republicans," said Democratic pollster Geoffrey Garin. "They have to try to do something to change the national narrative of the election, even if it means throwing their nominee right under the bus."

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AP Congressional Correspondent Erica Werner contributed to this report.