Senate Majority Leader Mitch McConnell's (R-Ky.) "single biggest regret of my time in Congress," he told Bloomberg News on Tuesday, is "our failure to address the entitlement issue." McConnell said that the mushrooming federal deficit, which the Treasury Department just said grew to $779 billion last fiscal year — 77 percent higher than when McConnell became majority leader in 2015 — is "very disturbing," but he blamed Medicare and Social Security spending, not the $1.5 trillion tax cut he steered through last year. "I think it's pretty safe to say that entitlement changes, which is the real driver of the debt by any objective standard, may well be difficult if not impossible to achieve when you have unified government," McConnell said.