Alabama Senate race is a big test for Mitch McConnell

The special Senate election in Alabama is a crucial test of President Trump's influence with Republican primary voters but Senate Majority Leader Mitch McConnell has the most to lose there on Tuesday.

Trump endorsed appointed Sen. Luther Strange in what is essentially a three-man contest, urging Republicans in Alabama via Twitter and pre-recorded, telephone "robo" calls to support him as Attorney General Jeff Sessions' permanent successor.

But it's McConnell's credibility on the line after his affiliated super PAC and associated nonprofit organization invested millions of dollars to boost Strange over Rep. Mo Brooks and Roy Moore, the former chief justice of the Alabama Supreme Court.

Surveys project that Strange and Moore will advance to in a late September runoff. But an upset could undercut McConnell politically heading into 2018 with his plans to protect incumbent Republicans and influence GOP primaries in red states where vulnerable Democrats are running for re-election.

"There's a universal desire to avoid the mistakes of the past when Republicans nominated candidates like Todd Akin, Sharron Angle and Christine O'Donnell, who all lost, and we don't want to do that again," a Republican insider said.