Tisei, the GOP's 2010 nominee, leads Tierney 45 percent to 40 percent in the Emerson College Polling Survey released Wednesday.
The 84-year-old congressman won one of the toughest primary challenges of his career.
The White House typically supports Democratic candidates, a spokesman said.
Brat said he doesn't want to be placed in the "cubbyhole" of a Tea Party Republican.
Former Marine Ben Thomas says in the ad for businessman Brian Ellis (R).
Establishment Republicans believe they've neutered the Tea Party for the foreseeable future.
Adriano Espaillat is holding out for a “complete and accurate tally.”
Rep. Doug Lamborn (R-Colo.) has narrowly avoided a primary upset.
Rep. Charles Rangel looks set to hold on for one more term in Congress.
Republican Richard Hanna has held on against his Tea Party opponent Claudia Tenney.