Massachusetts state Rep. Dan Winslow (R) has decided to run for the Senate in Massachusetts, he said Thursday. He's the first Republican to officially throw his hat in the ring.

"I’m going to be 100 percent running for the U.S. Senate,” Winslow, a former aide to then-Massachusetts Gov. Mitt Romney, told the Boston Globe. “This is a heavy lift. I’m going to give this race everything I’ve got.”