These days, Donald Trump may be willing to accept support from anywhere he can get it when it comes to big names in politics. However, the Republican presidential candidate might want to make sure his supporters don’t slip up and make avoidable mistakes when they hit the campaign trail on his behalf.

Take, for example, former New York City Mayor Rudy Giuliani, who had a couple slips of the tongue on Monday when he spoke before Trump at a rally in Youngstown, Ohio.  The statement that led to the most criticism? His assertion that the United States didn’t have “any successful radical Islamic terrorist attack in the U.S.” in the eight years prior to President Barack Obama taking office.

Of course, the Sept. 11, 2001, attacks in New York, Pennsylvania and Virginia were conducted in that same time frame. Giuliani, who was mayor of New York City at the time — his reaction to the events largely shaped America’s perception of him — seemed to gloss over that attack, though.

At least one survivor took to Twitter to criticize their former mayor for the statement.

Giuliani also told the Ohio crowd that Indiana Gov. Mike Pence has been a good governor of Ohio. Pence is running alongside Trump to become vice president.

As Talking Points Memo has pointed out, this isn’t the first time that Giuliani has received criticism for potentially offensive Sept. 11 comments. He caught some heat in 2010 when he tried to compare Obama to his predecessor, George W. Bush, and glossed over 9/11 while he was at it. At that time, Giuliani said that “we had no domestic attacks under Bush.”

Giuliani was referred to as “America’s mayor” following the terror attacks for his response. He frequently joins Trump on the campaign trail to promote the businessman’s  message.