50 Republican national security officials call him the most reckless candidate in history

Donald Trump is seeking to quell concerns he lacks the discipline or policy know-how to make a competent president, even as the list of fellow Republicans deeming him unfit for the Oval Office grows.

Maine Senator Susan Collins, a moderate long wary of Trump, became the latest Republican to announce her intent not to vote for her party's nominee. Days after rebuking Trump for insinuating Somali refugees in Maine were dangerous, Collins said on Monday she'd thought "long and hard" about whether she was obligated to support the GOP nominee and decided she could not.