Not since 2001 have Americans entered the holiday season with more trepidation, more nervousness, thanks to the Friday the 13th attacks on Paris. Thanksgiving weekend sends millions of Americans onto roads, into airports and train stations and shopping malls, soft targets for terrorists intent on wreaking havoc. On Monday, the U.S. State Department issued a worldwide travel alert, urging Americans to be vigilant in public places and on public transportation, especially during the holiday season. Wednesday, President Obama came to cameras, flanked by his homeland security team, to reassure the public that law enforcement and intelligence services will be on the job through the holiday to secure the country. He said there is currently no specific or credible intelligence of a terrorist plot. Is there a threat? Yes. What’s the likelihood of a terrorist attack in the U.S.? The experts say, extremely low.