As Obama has been President Obama watches the inaugural parade from the White House reviewing stand and prepares to attend numerous inaugural balls, law enforcement officials confirm that the the crowds that turned out for the day's festivities remained in check.
"Zero. There have been no inaugural-related arrest[s] reported by any of our law enforcement partners today," the Secret Service said, as of 5 p.m. ET.
A government official gave an unofficial estimate that the crowd topped 1.8 million, with 1.4 million on the Malland up to 400,000 in nearby streets.
The government doesn't give official crowd estimates, but it uses internal approximations to help dispatch resources.
Law enforcement officials had closed down public access to the parade route around 12:30 p.m. ET because it had begun to near its estimated capacity of up to 350,000.
And it was the massive crowd that presented a huge variable for law enforcement, though law enforcement sources said they do not have any information that there is an imminent threat to the inauguration festivities.
But out of caution, the Department of Homeland Security and the FBI issued a bulletin last night, expressing concern about "the threat individuals affiliated with al-Shabaab -- a radical Islamic extremist group active in Somalia -- may pose to the homeland, including locations and events of political significance, such as the upcoming presidential Inauguration."
The information, however, is "of limited specificity and uncertain credibility," the spokesman said, but "authorities at all levels are vigorously pursuing any lead relating to this threat information."
The DHS statement pointed out that large gatherings make for an attractive target for those looking to cause disruptions, but that officials "encourage the public attending inauguration events to go about their normal plans."
Noting that there is an "unprecedented level of security" for the inauguration, a DHS spokesman said that numerous federal law enforcement authorities are investigating and analyzing "recently received information about a potential threat on Inauguration Day."
ABC News recently reported that officials suspect that a group of men of Somali descent, who lived in the Minneapolis area, returned to Somalia for terror training. Officials have confirmed to ABC News that some of the individuals have returned to the United States.
The FBI and DHS bulletin notes that the men might have been associated with Shirwa Ahmed, a naturalized U.S. citizen who is believed to have blown himself up in a suicide attack in Somalia last October.
The bulletin states that officials released the information in an attempt to raise awareness and possibly obtain more information.