The Republican nominee, Sen. John McCain of Arizona, recycled that concern in the general election.
Sarah Palin, then McCain's running mate, accused Obama of "palling around with terrorists," in reference to his ties to the 1960s radical William Ayers.
For a time, the Sept. 11 attacks and subsequent political rhetoric forced Democrats to adopt more hawkish positions, Cardin and others said.
"As far as the overall national security posture, there has been virtually no difference between the parties," said Cardin, who opposed the Iraq war resolution as a member of the House in 2002. "It's hard to see a difference between the Democrats and the Republicans."
Cardin, who was elected to the Senate in 2006, is up for re-election next year.
Now, many of the political and policy changes that followed the Sept. 11 attacks are being reversed. The budget agreement struck last month to resolve the crisis over the nation's debt ceiling, for instance, included $420 billion in cuts to defense spending over the next decade. Those cuts were endorsed by House Republicans, who had long held defense spending sacrosanct.
If Congress cannot agree on a long-term plan to reduce the debt by November, another $500 billion in defense cuts would occur automatically.
As Obama winds down the war in Iraq and redefines the nation's role in Afghanistan, the U.S. involvement in the NATO intervention in Libya has divided Republican lawmakers and the GOP presidential field — a break from the broadly hawkish stance that has long characterized the party.
Former Massachusetts Gov. Mitt Romney supported the Libya mission, with criticism of how Obama has handled it. Former Utah Gov. Jon Huntsman Jr. and Minnesota Rep. Michele Bachmann have opposed it. Texas Gov. Rick Perry has tended to tread lightly on the subject.
Sept. 11 had more subtle political implications beyond defense and security, experts say. Jennifer Lawless, director of the Women & Politics Institute at American University, believes the attacks reduced voters' willingness to support female candidates to the lowest point in decades.
Donald F. Kettl, dean of the University of Maryland School of Public Policy, speculated that the attacks and subsequent attempt to tackle terrorism have led to more infighting within the political parties.
Sept. 11 "escalated the rhetoric but merged policy positions, since everyone was opposed to terrorists — but we have had an increasingly hard time figuring out what to do about them," Kettl said. "It's shadow boxing on steroids."
He noted that the cost of the wars is a major contributor to federal budget deficits, which gave rise to the tea party movement.
"It's not a straight line" that links the conservative movement to Sept. 11, "but there's unquestionably a connection."
Despite the rhetorical bickering, the public has largely given both Obama and President George W. Bush high marks on fighting terrorism, even when voters disagreed with them on other issues.
Last month, six in 10 respondents to an Associated Press poll said the phrase "he will keep America safe" described Obama "very or somewhat well."
Rep. C.A. Dutch Ruppersberger, the top-ranking Democrat on the House Intelligence Committee, credited the Bush administration with helping to retool the nation's military for the modern threat of terrorism. But the Baltimore County lawmaker also suggested that some of the defense cuts proposed by the Obama White House and others are long overdue.
"We were used to battling nations, and we had to change our way of operating," Ruppersberger said.
"It seems we've lost sight that we still have men and women in Afghanistan and in Iraq," he said. "We can't allow al-Qaida to use Afghanistan. On the other hand, we can't be the sheriffs for the whole world."
Sense of Sept. 11
Opinion polls show how public attitudes about Sept. 11 have changed over the past decade.
How people rate the U.S. government's effort at reducing the threat of terrorism:
Date: Very or fairly well//Not well
Source: Pew Research Center
Percentage of people who think it "very likely" that there will be another terrorist attack in the United States within the next few months.
Source: New York Times/CBS News poll