MANCHIN’S UNEXCUSED ABSENCE…. It was an important day on Capitol Hill yesterday, with the Senate taking up some key measures that were years in the making. Sen. Ron Wyden (D-Ore.), who was expected to miss the proceedings with pre-op tests before cancer surgery tomorrow, made a point to be there. Sen. Joe Lieberman (I-Conn.), an orthodox Jew, worked on the Shabbat.

So it came as something of a surprise when one member of the Senate Democratic caucus couldn’t quite make it to work yesterday — and offered an underwhelming explanation for his absence.

There was one Democratic senator who missed today’s crucial votes on Capitol Hill: West Virginia’s Joe Manchin, who was elected just last month.

So where was Manchin when the Senate finally passed the “don’t ask, don’t tell” repeal and took one last shot at the DREAM Act immigration bill?

At a holiday party.

“Sen. Manchin and his wife Gayle planned a holiday gathering over a year ago with all their children and grandchildren as they will not all be together on Christmas Day. While he regrets missing the votes, it was a family obligation that he just could not break,” Manchin spokeswoman Sara Payne Scarbro said.

By all appearances, Manchin’s vote wouldn’t have affected any of the outcomes, and based on his stated positions, Manchin would have voted with Republicans anyway.

But it’s the principle here that rankles. Call me old fashioned, but I think senators should show up for work, and if they can’t, the excuse should be better than “Christmas party.”

Indeed, Ben Smith noted that Manchin wouldn’t even have far to go to return home after the day’s proceedings: “United Airlines Flight 7795 departs Washington Dulles this evening at 5:40 PM and goes direct to Charleston, W.V., where Manchin lives, arriving at 7:16 PM.”

He could have voted and been home in time for pictures and eggnog.

The National Republican Senatorial Committee’s spokesperson said, “I’m sure that most Senators, as well as the hundreds of staffers who had to come to work today, would have rather been at a Christmas Party like Joe Manchin. But perhaps in Joe Manchin’s world today was a win-win — not only was he able to skip work and party, but he was also able to avoid voting on two very sensitive political issues. For a Senator who has only been on the job a few weeks, Manchin’s absence today, and the apparent lack of seriousness with which he takes the job he was elected to do, speaks volumes.”

In most instances, the NRSC takes some pretty cheap shots at Democrats. In this case, the Dem deserves it.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.