AP Photo/J. Scott ApplewhitePresident Donald Trump, a Republican, publicly attacked two GOP senators in a series of tweets Thursday morning. "Great to see that Dr. Kelli Ward is running against Flake Jeff Flake, who is WEAK on borders, crime and a non-factor in Senate. He's toxic!" Trump tweeted, taking a shot at the junior Arizona senator. Flake is up for reelection in 2018 and is considered one of the more vulnerable GOP senators in the next election cycle.