It's a rare find this midterm campaign: An ad from President Obama on behalf of a Democrat in danger of losing to a Republican.

But that's what you'll find in Nevada's 4th district, where Obama just cut a radio ad for Rep. Steven Horsford (D), who is battling a late flurry of Republican outside spending against him.

In the ad, released Thursday, Obama casts Horsford as a bipartisan dealmaker in Congress.

"I know that sometimes politics can seem focused on small things. Middle class families need their leaders to do big things," says Obama. "But your congressman, Steven Horsford, hasn’t let Washington gridlock get in his way."

Obama won Horsford's central Nevada district by 10 percent points in 2012. For most of this cycle, Horsford, who co-chaired Obama's 2008 campaign in the state, hasn't been viewed as especially vulnerable.

But the conservative group Crossroads GPS has spent big toward the end of the race trying to help Republican Assemblyman Cresent Hardy spring an upset, forcing the Democratic Congressional Campaign Committee to pour in $360,000 in late ad spending on Horsford's behalf.

Part of the Crossroads attack pattern has been to tie Horsford to Obama's agenda, as in this ad:

Early voting numbers have been encouraging for Republicans. As Nevada Politics expert Jon Ralston tweeted, Horsford's ad is a recognition that he needs to boost turnout among Democrats: