See this article. 50 of them signed a letter that said the following:
“We are convinced that [Trump] would be a dangerous President and would put at risk our country’s national security and well-being. Most fundamentally, Mr. Trump lacks the character, values, and experience to be President. He weakens U.S. moral authority as the leader of the free world. He appears to lack basic knowledge about and belief in the U.S. Constitution, U.S. laws, and U.S. institutions, including religious tolerance, freedom of the press, and an independent judiciary.”
See the rest of the letter at the link.