Active-duty personnel, veterans, and their families are the second-largest voting bloc after Hispanics, and the only group that consistently votes Republican.

The limited available polling suggests Trump has weaker support than John McCain or Mitt Romney, the party’s two most recent presidential candidates, said John Noonan, who was national security adviser for Romney.

Trump is up 14 points over Clinton with veterans, 53 percent to 39 percent, according to a Fox News poll released Wednesday. McCain was 22 points ahead at this juncture in the 2008 race with registered voters who had served in the U.S. military; Romney was up 24 points in May 2012, Gallup polling showed.

“Trump will have to over-perform with veterans to overcome his deficiencies with Hispanics, African-Americans, women, and college-educated whites,” Noonan said.