Story highlights "And he wants to help Hillary fill another chair on the Supreme Court," the ad says

The NRA has long argued that the Senate is crucial given its role in court appointments

Washington (CNN) The latest Republican advertiser to imply Senate Republicans must win in order to check the power of a presumed President Hillary Clinton: the National Rifle Association.

The NRA, which has been one of the most vociferous defenders of Donald Trump on television, is unveiling an advertisement in Indiana that raises the specter of a Senate that allows Clinton to exercise unlimited control. It is a message that Republicans have been testing nationwide in recent weeks as they work to insulate down-ballot Republicans from the damage wrecked by Trump's fall in the polls.

"Bayh used this chair to help Obama put anti-gun liberals on the Supreme Court," says the narrator, as the screen flashes to a row of seats in the US Senate. "Now Evan Bayh wants back in the Senate. And he wants to help Hillary fill another chair on the Supreme Court."

Bayh, once thought to gallop easily back into his old Senate seat, is fighting to beat back a stronger-than-expected challenge from Rep. Todd Young. The NRA is spending another $500,000 on the ad to boost Young in the state, where Clinton is broadly unpopular.

Republicans, from the Chamber of Commerce to the Senate Leadership Fund to individual Senate campaigns, have begun preparing from a possible wipe-out at the top of the ticket with a similar strategy. But Republicans are discovering that it's not an elixir: One GOP operative who polled an advertising campaign in Wisconsin and Pennsylvania that called for a counterweight to Clinton found that the Democratic nominee was simply too popular there for that strategy to succeed.

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