Phoenix Mayor Greg Stanton warned Tuesday that if President Trump changes his mind about pardoning former Maricopa County Sheriff Joe Arpaio and announces it during the rally, protesters could get violent.

"If he were to go against what his press secretary said today, it would be a very bad thing and a potentially very volatile thing here in Phoenix," Stanton told CNN host Andeson Cooper two hours before the rally. "He might do that. There's nothing we can do about that, other than his press secretary indicated it's not going to occur tonight in this politicized environment, so shortly after his failure of moral leadership, after the tragedy in Charlottesville."

Stanton agreed with Cooper that it would not be surprising if Trump, feeding off the energy of his supporters, decided to surprise the crowd with the announcement. Cooper warned doing so would send a clear message about Trump's interests.

"And for the president to do that at a campaign rally in front of 10,000 people would -- the only purpose would have been to inflame passions. And, yes, I was very concerned about what that might do on the streets of Phoenix," Stanton added.

Earlier Tuesday, Stanton asked Trump to delay his trip to Arizona following the violent protest in Charlottesville two weekends ago.

"President Trump's response to Charlottesville reminds us that the words and actions of our political leaders in the wake of tragic events matter," Stanton wrote in an op-ed published Monday. "America is hurting. And it is hurting largely because Trump has doused racial tensions with gasoline. With his planned visit to Phoenix on Tuesday, I fear the president may be looking to light a match."

"That's why I asked the president to delay his visit. It's time to let cooler heads prevail and begin the healing process," Stanton added.