They work in the same building. They slog through the same rigorous travel schedule. Along the way, they often cross paths several times a day.
But Senators and have barely spoken to one another – at least in any meaningful way – for months.
The tension between the two Democratic presidential hopefuls, which spilled over into public view during the past two weeks, has been intensifying since January. It is clear, as the candidates approach a mid-point in their fight for the nomination, that the genteel decorum of the Senate has given way to the go-for-the-jugular instinct of the campaign trail.
As the Senate held an unusually late session of back-to-back votes on Thursday evening, the two rivals kept a careful eye on one another as they moved across the Senate floor.
For more than two hours, often while standing only a few feet apart, Mrs. Clinton and Mr. Obama never approached one another or exchanged so much as a pleasantry. In the clubby confines of the Senate, even the fiercest adversaries are apt to engage in the legislative equivalent of cocktail party chit-chat.
The Clinton-Obama watch has become something of a parlor game, and not only for the scribes sitting in the gallery above the Senate floor. The strained relationship between the two Democratic hopefuls also has drawn the attention of their colleagues, who are loathe to take sides, but often will rush over to chat with Mr. Obama or Mrs. Clinton if either is spotted standing alone.
Consider a scene from the Capitol on Thursday, where lawmakers worked through a long stack of amendments before passing children’s health insurance legislation (an issue presidential contenders could hardly skip).
It was a few minutes after 8 p.m. when the side doors of the Senate swung open and three Democratic candidates walked through.
Mrs. Clinton, of New York, and Senator of Connecticut came first, laughing and smiling as they made their way to the Democratic side of the aisle. A few paces behind was Senator of Delaware, who quickly joined the other two in a light moment. (Earlier, Mrs. Clinton and Senator , an Arizona Republican, had been trading warm banter near the front of the Senate floor, which takes on the air of a schoolyard during marathon voting sessions like these.)
Mr. Obama entered the Senate floor alone. He glanced at the other three, pulled out his Blackberry and paused for a few seconds before walking to the third row and taking a seat next to three freshman senators. As the evening passed, Mr. Obama and Mrs. Clinton each spoke with several in the room and to nearly every Democrat -- except each other.
It wasn’t always this way.
When Mr. Obama was running for the Senate, Mrs. Clinton waited out a lightning storm on a tarmac to fly to Chicago for a fundraiser on his behalf. After he arrived in Washington in 2005, he studied her first year in office and worked to keep a similarly studious – yet low – profile. After Hurricane Katrina, he joined Mrs. Clinton and former President as they visited storm evacuees in Houston, with Mr. Obama walking a few paces behind out of deference to the leading names of the Democratic Party.
The relationship began to change, according to several Democrats who are friendly to both senators, when Mr. Obama began musing aloud about a presidential bid. The day he opened his exploratory committee, several Senate observers said, he extended his hand and said hello on the Senate floor. She breezed by him, offering a cool stare.
One week later, following the State of the Union address, the two senators found themselves doing a back-to-back interview on CNN. Mr. Obama went first, with Mrs. Clinton pacing a few feet away. Finally, an aide escorted her completely around the rotunda of the Russell Senate Office Building, avoiding walking directly by Mr. Obama.
Many Senate observers, even those close to Mrs. Clinton, say they believe she set the less-than-collegial tone. But Mr. Obama offered a glimpse into his own competitiveness two years ago when a Chicago television reporter who had come to Washington to interview Mr. Obama informed him that he had snagged a hallway interview with Mrs. Clinton.
“I outpoll her in Illinois,” Mr. Obama said. After realizing his remark had been overheard, he said: “That was a joke!”
Now, with both of the candidates under Secret Service protection, their entourages are larger and they are less likely to have a face-to-face encounter, except on the Senate floor, where they walk alone. In fact, one of the last times an impartial Senate observer could remember the two standing together – without tension – was when lawmakers gathered around a TV in the Cloakroom as announced her cancer had returned.
When the cameras capture them together, they can be gracious and relaxed toward each other. At the end of the most recent Democratic debate, when the candidates were all asked to say what they like and dislike about one of their opponents, Mrs. Clinton said of Mr. Obama, “I admire and like very much Barack, as I do with all of the candidates here.”
A moment later, Mr. Obama defended Mrs. Clinton against a bad fashion review that former Senator had jokingly directed at her. “I actually like Hillary’s jacket,” Mr. Obama said.
Aides to both senators declined to discuss the tensions. But as he walked through the Capitol on Thursday, Mr. Obama paused for a moment to answer a question about their relationship.
“She’s said hello a couple times,” Mr. Obama said, a slow grin spreading over his face as he walked away. Turning back, he added: “It’s been fine.”