As it appears increasingly likely that Hillary Clinton will be the next president, many conservative outside groups are stressing the importance of maintaining Republican control of the Senate as a check on her presidency.

The Senate Leadership Fund, a super PAC allied with Senate Majority Leader Mitch McConnell, is putting $25 million into six key Senate races in an effort to counter the Democrats focusing their firepower on down-ballot races, CNN reported. 

An ad from the National Rifle Association’s Institute for Legislative Action warns that Democratic former Sen. Evan Bayh, who’s seeking his old seat against GOP Rep. Todd Young in Indiana, would help Clinton fill another seat on the Supreme Court.

Similarly, an ad from the U.S. Chamber of Commerce promoting Republican Sen. Kelly Ayotte’s re-election in New Hampshire opens with an empty debate stage and the White House.

“No matter who the next president is, New Hampshire needs a strong voice in the U.S. Senate,” the narrator says.

The chamber has previously clashed with Republican presidential candidate Donald Trump, particularly on the issue of free trade.

An ad from the Senate Leadership Fund targeting Missouri Democrat Jason Kander says, “One Hillary in Washington would be bad enough,” and another ad from the group calls him a “carbon-copy liberal.”

The fund will spend $7.5 million on the open Nevada race on behalf of GOP Rep. Joe Heck, and $5 million in Pennsylvania, where Democratic challenger Katie McGinty and incumbent Republican Sen. Patrick J. Toomey are running neck and neck.

The Senate Leadership Fund released an ad this week accusing McGinty of corruption, including allegedly giving money to companies that paid her husband. The narrator says, “Hundreds of Pennsylvanians got screwed but McGinty got rich.”

The fund also plans to spend $4 million on the Bayh-Young race in Indiana and smaller amounts in Missouri, New Hampshire and North Carolina.

In North Carolina, the group released an ad hitting Democrat Deborah Ross who’s put up a surprisingly strong challenge to two-term GOP incumbent Sen. Richard M. Burr. The ad alleges that during Ross’ time as director of the North Carolina American Civil Liberties Union she did not support a veteran’s right to fly a flag but opposed a ban on flag burning.