Steven Arroche and Sarah Parker socialize in Lafayette Park, across from the White House, in Washington, DC on Nov. 6. (Bonnie Jo Mount/The Washington Post)

After media outlets began declaring that President Obama had won a second term Tuesday, the blare of car horns and cheerful shouts of “Obama!” could be heard along the blocks surrounding the White House.

Supporters filled both sidewalks of 16th Street as they descended upon Lafayette Square outside the presidential mansion about 11:30 p.m. The crowd started small with a half-dozen or so people trickling in, but it grew to a throng of hundreds as police erected barricades on Pennsylvania Avenue.

“Four more years! Four more years!” the crowd chanted.

Other revelers checked their phones, continuing to seek updates on poll results from Florida or Colorado. Video screens and camera flashes lit up the crowd.

Earlier in the night, as election results came in and the after-work crowd in downtown Washington filed into the bars and election-watch parties, the talk was all politics and the mood turned increasingly sour for supporters of Mitt Romney.

Amid martinis, appetizers, and the competing red and blue election-season cocktails, patrons at the Off the Record bar in the Hay-Adams hotel watched early returns roll in from CNN on two flat-screen TVs. Republicans including Jon Rand, a 39-year-old mortgage broker, were pessimistic even after only a few states had been called. He expected Romney to lose and considered it a missed opportunity for his party.

“I just think that he wasn’t that energetic. He wasn’t able to get more people behind him, to jump on board, which is unfortunate given the state of the country,” Rand said.

Along the 2000 block of 14th Street NW, which was a similar eruption of outdoor celebration four years ago, the mood turned from cautious to buoyant as Obama’s electoral votes piled up. A line formed outside the jammed progressive hub Busboys and Poets, which had Rachel Maddow and MSNBC holding court on the big screen.

Kate Shaw, 27, and Courtnay Davis, 29, queued up to have a glass of wine and soak in the experience of communal hand-wringing.

“I think four years ago we just knew the excitement and momentum,” said Davis, a meeting planner from Rockville. “And now we Just. Don’t. Know.”

As the night wore on, Obama supporters began to feel more confident. At 11 p.m. in the Madison Hotel bar on 15th Street, Mario T. Price, an African American lawyer from Silver Spring, and a friend finished their drinks and focused on watching the returns. He said he volunteered for Obama four years ago in Virginia but decided not to this time around.

“There were certain folks who felt disappointed that the magic didn’t happen as quickly as they would have hoped,” Price said. He cited Obama’s decision to focus on health care reform before fixing the economy as something that had opened the president up to attacks.

“That really helped to rally the right,” he said.

As Obama closed in on the win, cheers from the crowd of “Si, se puede!” — “Yes, we can!” — drowned out a few boos from Romney supporters in a packed house at Barcode on L Street downtown. “In Texas, our elections aren’t this exciting,” said San Antonio resident Darcy Hardy, 53. “We get pumped up, but never like this.”

When MSNBC called the election for Obama about 11:20 p.m., the Busboys and Poets crowd erupted in cheers of “Four more years!” The restaurant’s owner, Andy Shallal, said he saw nearly the same enthusiasm for Obama as four years ago. “I think that people still want to believe. That idea of hope is still out there,” he said.

People’s expectations for the president’s next four years in office, however, may be tempered.

“I think that people this time are saying that they’re not just going to help get him elected but help hold him accountable,” he said. “And I think they are ready to get to work.”

Rachel S. Karas and Dan Zak contributed to this story.