NEW YORK -- This week, 46 million people will travel in the United States, and they will see extra officers, patrol dogs, and guns at virtually every airport, train station and tourist destination in the country.
According to a new poll, 83 percent of registered voters believe a large scale terror attack in the U.S. is likely in the near future.
Homeland Security Secretary Jeh Johnson said his agency is ready for anything.
"I always hesitate to rank threats, but the potential copycat, the lone-wolf actor is one that we're continually focused on," he said.
Lines at the airports will be longer, and slower. The TSA said it will handle 25 million passengers this week, with enhanced screenings.
New York passenger Sherry Tropin left for Miami on Sunday.
"We're all a little bit more aware of the increased security now and that people might be a little more nervous," she said. "But at the same time we're still traveling."
If travelers are nervous, so are the airlines. Just this week, Southwest delayed or diverted three flights.
In two cases, passengers were afraid when fellow fliers spoke Arabic.
On Sunday, three passengers said to be acting suspiciously on a flight from Indianapolis to Los Angeles forced a diversion to Kansas City.
Phony bomb threats redirected three flights this week from the U.S. headed overseas, including a Turkish Airlines Flight to Istanbul on Sunday morning.
Also Sunday morning, in New York City, police held a three-hour active shooter drill in the city's subway system. For the first time, their drill included an attacker in a suicide vest.
"We have now beefed up our resources that will be in a position to handle a significant number of events going on simultaneously, and sequentially," said Police Commissioner Bill Bratton.
Department of Homeland Security said there are no credible threats anywhere in the U.S.
"My message to the public in this holiday season is while we urge you to continue to travel, go to public events, go to public places, and know that our folks are on the job," Johnson said.
Extra security measures are also in place for overseas flights.