As Americans head out for the Fourth of July holiday weekend, they find stepped-up security at the nation's airports since the recent terrorist incidents in Great Britain.
There are more armed officers and additional canine units on patrol, and random searches of cars. Airport security officials said they would also be moving drivers along more quickly and responding fast to any reports of suspicious or abandoned vehicles.
The United States has also increased the number of air marshals on overseas flights.
The alert level at the nation's airports remains orange, signifying a high risk of a terrorist attack, but the threat level for the country remains yellow, which means an elevated risk of an attack.
Department of Homeland Security officials insist there is no need to raise the threat level outside airports.
Homeland Security Secretary Michael Chertoff, speaking on "Good Morning America" today, said, "We do not have any specific, credible information about an attack directed at the United States."
Department spokesman Russ Knocke spoke to ABC News about making any changes to the threat level. "We're very serious about our responsibility to be clear and sober about an increase or an adjustment and why it's being made. We're not going to make an adjustment to the threat level if there is no credible intelligence to support it."
Knocke insisted that politics plays no role in determining whether to raise or lower threat levels, saying, "that does not factor into our decision."
Some question whether the department, in implementing stepped-up security in the past few days, has raised the threat level to the next level in practice if not in name.
Knocke and others denied that. They said they would be taking significantly more measures, both visibly and behind the scenes if security was increased to the next and highest level, which is red. Red signifies a severe risk of a terrorist attack.
Security measures under a red threat level could include barricades in front of airports, checking all vehicles, and National Guard troops in airports.
U.S. officials did raise security to the red level for a few days last August but only for flights from the United Kingdom to the United States. That was after the British foiled an alleged plot to use liquid explosives to blow up numerous flights from the Great Britain to the United States.
The ramifications of that plot are still felt by U.S. air travelers, who are restricted in the amount of liquids they can bring onboard.
One federal security official told ABC News that raising threat levels has to be a "very deliberate step for well-articulated reasons. We want to keep the powder dry," he said. "We want it to be meaningful. When we go into the next zone, we must have hard evidence."
Transportation Security Administration spokesman Christopher White said "the difference between code orange and code red is that red means an attack is imminent. Since 9/11, no U.S. airports have been at code red. "We are not at red, and [don't expect] to go to red at this time," White said.
ABC's Brian Ross and Pierre Thomas have reported that U.S. intelligence has grown increasingly worried about an attack this summer against Western targets, possibly in the United States.
According to Ross, government sources have also indicated that U.S. intelligence officials received intelligence reports two weeks ago warning of terror attacks in Glasgow and Prague against "airport infrastructure and aircraft."
Chertoff denied that today on "Good Morning America," saying, "We didn't have any specific, credible information about an imminent attack in Glasgow."
One former CIA and State Department counterterrorism official believes the United States is justified in keeping the terrorist alert at its current level. He believes officials are overreacting by increasing security at the airports.
Larry Johnson, who now works as a terrorism consultant, said, "doing this is more about politics than security ... there is no reason to do this."
Johnson said, "It would be one thing if they had intelligence showing people are planning on loading a car with an IED [mprovised explosive device] and driving into an airport. We don't have that kind of intelligence."
"The reality," Johnson said, "is that these kinds of incidents are very infrequent and very rare ... and good law enforcement and intelligence can go a long ways toward thwarting these things."
Brian Jenkins, an analyst at the Rand Corp., believes the government is correct to increase security. "It's just a matter of prudence," he said. "Let's lean forward a little in the foxhole and take it up a notch."
Jenkins said events like those in Great Britain often inspire copycats and hoaxes. "Whether it's a genuine jihadist or a malicious crankster, they could think this is the time to act," he said.
He also believes the increased security may help reassure the public, and that if the Department of Homeland Security failed to increase security and an "event occurs, then people will say, 'Why didn't you do something?'"
Jenkins agrees with Johnson that there is always a political calculation to decisions to increase — or decrease — security.
Johnson believes that adding patrols and searching cars have a measurable effect on security, but he insisted, "we need to be far less reactive, or react when we know there is something we can do to truly change the threat picture and make people safer, as opposed to inconveniencing people over a holiday weekend."