Convention Security Concerns Shift to Philadelphia

— -- One convention down, one more to go. Thousands of police and federal agents who were in Cleveland last week for the Republican National Convention are now in Philadelphia for another week of long days and heightened vigilance.

The recent attacks on police in Dallas and Baton Rouge, Louisiana, as well as the terrorist attack in Nice, France, are “certainly a reminder you’ve always got to be ready for any scenario,” according to Secret Service Director James Clancy.

“We should have a plan already in place for whatever we may be confronted with,” Clancy told ABC News’ Pierre Thomas in an exclusive interview ahead of the Democratic convention in Philadelphia.

For weeks, top U.S. officials have been warning that radical activists drawn to the political conventions could mar otherwise peaceful demonstrations with violence.

"I am concerned about the prospect of demonstrations getting out of hand, and concerned about the possibility of violence," Homeland Security Secretary Jeh Johnson told lawmakers earlier this month.

Johnson said the Department of Homeland Security alone sent about 3,000 personnel to the RNC and will do the same for the DNC. That includes personnel from the Secret Service, the Transportation Security Administration, Customs and Border Protection and the U.S. Coast Guard.

In addition to the DHS personnel, thousands of other federal authorities and thousands of state and local authorities are helping to protect each convention. And they are backed up with aerial support and a massive setup of barriers and fences to restrict access to venues – an unprecedented level of security despite law enforcement knowing of no specific, credible threat to the conventions.

The convention in Philadelphia, however, presents new and different challenges than those facing officers and agents in Cleveland.

“They're two very different venues,” Clancy said. “The landscapes are much different.”

And even for experienced security officials involved, tensions run high until the candidates accept their party’s nominations and all the attendees and demonstrators go home safely.

“Absolutely I do get butterflies, absolutely feel the anxiety,” Clancy said of those last minutes inside the convention halls.

“You continue to go back over your plan,” he added. “You never think you’ve got your plan perfectly in place.”

According to Clancy, even if all goes well in Philadelphia, he won’t feel the pressure lifted until a full day after the convention ends.

“It usually takes about 24 hours after an event … you got to sleep on it a few hours,” he said.