It's the oil capital of the country and home to the Bush family. So more than most cities in the country, Houston considers itself a bull's-eye for terrorists.
Downtown boulevards are lined with the headquarters of gas and oil companies that are believed by many people, especially abroad, to influence U.S. policy toward oil-rich Iraq. Below ground, a labyrinth of steel pipelines carries crude oil and natural gas. Overhead, jets soar above George Bush Intercontinental Airport, named for the president who ordered attacks on Iraq 12 years ago and the father of the president who is leading the new charge.
"When you look at the points of vulnerability, unfortunately Houston has all of them," Mayor Lee Brown said. "We have the port, the petrochemical plants, the medical center, the airport, Johnson Space Center. We are the energy capital of the world."
Signs of the perceived threat are evident around the city. Private security has been doubled at the Port of Houston, the country's second-largest hub of foreign tonnage. Additional armed guards and off-duty sheriff's deputies have been hired to patrol aboveground pumping stations for one major natural gas company, according to a company spokeswoman who spoke on condition of anonymity. And at Dynegy Inc. headquarters in the business district known as Energy Alley, the ranks of the company's security force have swelled.
"The Bush family has ties to Houston, and former President Bush and his family live here," said Blake Young, Dynegy's executive vice president of administration and technology. "That gives some heightened awareness to people looking at Houston as a potential target."
Harris County Sheriff Tommy Thomas has not yet ordered his deputies to work 12-hour shifts, but they are on "high alert."
"Those of us who deal with it on a daily basis, we definitely feel like we could be a prime target, more than the other big cities around the country," said Thomas, whose jurisdiction includes Houston.
No threats have been leveled against the city, according to the FBI, but agents would be "naive" if they didn't take into account the city's link to the Bush family, said Bob Doguim, the bureau's spokesman in Houston.
"Whoever doesn't know that Daddy Bush lives in Houston lives under a rock," Doguim said.
Concern extends to the museum district, a center of peace vigils and antiwar protests.
"I mean, how many transnational oil companies are headquartered downtown?" asked Russell Moore, 29, a bartender who has joined in recent peace marches. (The answer is 44.) "Seems to me those terrorists like their symbolism."
Adding to the uneasiness is one of Houston's quirks -- no land-use zoning, which means homes are near chemical refineries. Houston City Councilwoman Carol Alvarado represents a pie-shaped district that includes homes, a Goodyear tire plant and a Valero Energy Corp. refinery. It also includes the city's smaller airport, Houston Hobby, and the Port of Houston.
Everywhere she looks, she said, there are points of vulnerability.
From office buildings to water treatment plants to the nuclear plant 100 miles south of Houston, security upgrades now correspond to the Office of Homeland Security's orange threat level.
For some, though, that isn't enough.
"My mom didn't want me to come here because of the association with oil," said Caleb Everitt, a 20-year-old college student who lives about 30 miles north of the city. He was in Houston to visit a friend.
"She thinks this is going to be one of the first places to be attacked."