WASHINGTON >> As President Barack Obama faced public criticism over his Oval Office address on terrorism this month, one lawmaker took a private moment during a holiday party at the White House to reassure the commander in chief.

“That was a good speech you gave last night, Mr. President,” Rep. Steve Cohen, D-Tenn., told Obama as he stopped to have his picture taken with him in the photo line at the black-tie congressional ball last week. “It’s hard to be the grown-up in the nation.”

It was one of hundreds of secondslong interactions that the president and the first lady, Michelle Obama, are having with guests at some of the 20 holiday receptions that crowd their lives each December. Eagerly anticipated, sometimes politically fraught and often agonizingly awkward, photo-line banter with the president has become a staple of the holiday season in Washington, where yuletide ritual meets professional opportunism — all in the course of about 6 seconds.

“You need to bomb the Iranian nuclear facilities,” former Rep. Michele Bachmann, R-Minn., told Obama last year in one such brief exchange, taking advantage of her last holiday soiree with the president before leaving Congress. The president told her it was not that simple, according to an account she later gave to The Washington Free Beacon.

Jokes are told, interviews requested, and unsolicited advice given to the president along with handshakes, high fives and the not-infrequent deer-in-headlights stare from a speechless guest. Family members are introduced — and often star-struck.

“To staff the president and first lady at the holiday photo line is to observe humanity in its most awkward state,” said Bill Burton, a former top press official in Obama’s White House.

Obama, who barely tolerates the schmoozing that is presidential tradition, does far fewer receiving lines than his predecessors. George W. Bush and his wife, Laura Bush, worked a photo line at each of the 25 holiday parties he hosted in 2008, his last year in office, but the Obama White House has eliminated all but a handful. Congress and the news media are among the groups that still stand in line for the presidential grip-and-grin.

The Obamas cut back the ritual in part because it is demanding and time-consuming — each line lasts as long as 2 1/2 hours — and in part because they wanted to give as many people as possible an opportunity to visit the White House.

“It’s just long and tiring and pretty hard to get through,” Tina Tchen, Michelle Obama’s chief of staff, said in an interview. “We also had to balance, from a staff perspective, having photo lines versus how many people we could get in.”

By eliminating the receiving line, Tchen said, the White House is able to invite twice as many guests to a party. But the private backlash has been fierce in some quarters.

The moment can be about much more than a picture. The congressional party at the White House last week was Barack Obama’s first face-to-face encounter with House Speaker Paul D. Ryan, R-Wis., since Ryan assumed his post in November. If the two spoke about the year-end budget agreement needed to prevent the government from shutting down, neither side would say so.

Drama unfolds in the photo line as well. In 1999, a year after managing impeachment proceedings against President Bill Clinton, Rep. James E. Rogan, R-Calif., lined up with his wife to be photographed with the president and Hillary Clinton.

When the Rogans’ turn came and their name was announced, he said in an interview, Bill Clinton “kind of looked at me funny for a moment, then he let out this big sigh and gave me a huge smile and said, ‘Jim, thanks for coming. I’m really glad you’re here. Merry Christmas.’”

“It felt like he and I had kind of patched it up,” Rogan said.

But Hillary Clinton, who was distracted while saying goodbye to the previous guest, was not as friendly. When she finally noticed Rogan, her eyes widened with surprise, he said, and she gripped his hands tensely. “There was some iciness there and a bit of a grimace,” he said.

Ann Compton, who covered the White House for 40 years for ABC News, said she almost always treated the photo as a crucial, although brief, opportunity to buttonhole the president with a question only he could answer. The exception was at George H.W. Bush’s 1992 holiday party, a somber affair because he had just lost in his re-election campaign and was preparing to leave the White House.

Compton said she and her husband opted not to join the photo line, but they then encountered the Bushes as they were posing with the last guests.

“Barbara Bush looked at me and said, ‘You weren’t in line,’” Compton recalled, “and I said, ‘Mrs. Bush, that was our Christmas present to you.’”