The former New York mayor on Monday endorsed Kentucky Secretary of State Trey Grayson in the GOP Senate primary, and he proceeded to go after Paul, Grayson's primary opponent, in some pretty stark terms. He didn't mention Paul by name, but the target is clear.

Following a line of attack Grayson has used against Paul, Giuliani said Grayson "is not part of the ‘blame America first’ crowd that wants to bestow the rights of U.S. citizens on terrorists and point fingers at America for somehow causing 9/11."

“Kentucky needs a senator who understands the threat posed by our enemies abroad," Giuliani said. "I witnessed firsthand the destruction and loss of life our enemies can cause. Like me, Trey Grayson knows we must stay on offense against terrorism, and he supports using all the essential tools we have in that fight, including monitoring the conversations and activities of suspected foreign terrorists as allowed by the Patriot Act."

Grayson has rolled out late endorsements from former Vice President Dick Cheney, former Sen. Rick Santorum (R-Pa.) and now, Giuliani. Paul, the son of Rep. Ron Paul (R-Texas) and a favorite of the Tea Party crowd, last week nabbed the backing of retiring Sen. Jim Bunning (R-Ky.).

Paul campaign manager David Adams responds: "Another pro-abortion liberal Republican endorsing Trey Grayson is just more bad news for him. We'll stick with Rand PaulRandal (Rand) Howard PaulGOP senators call for probe of federal grants on climate change Overnight Health Care — Presented by the Association of American Medical Colleges — Key ObamaCare groups in limbo | Opioids sending thousands of kids into foster care | House passes bill allowing Medicaid to pay for opioid treatments US watchdog: 'We failed' to stem Afghan opium production MORE's conservative endorsements from Sarah Palin, Senator Jim Bunning, Steve Forbes, Northern Kentucky Right to Life and Gun Owners of America."

The primary is May 18.