Nearly a week after Election Day, the party balance in the Senate is all but set in stone. Democrats -- somewhat amazingly -- padded their majority, and with no yet-to-be-called races or looming recounts, appear headed for a 55-45 advantage in the upper chamber.

That is, if Sen.-elect Angus King (I) of Maine caucuses with the party. 

King's forthcoming decision is about the only loose end left in what's been an unpredictable two-year battle for the Senate. But his decision likely won't surprise anyone. He's widely expected to join the Democratic caucus and there are a number of reasons why it's a virtual certainty that he'll do so. 

(Robert F. Bukaty/AP)

First, the latest on King's public position on the matter. During the campaign, the independent former governor consistently said he had not made a decision about which side he would caucus with. As of Monday morning, that's still what he was saying. King spokeswoman Crystal Canney told The Fix that King is still mulling his options and will be meeting with both Democrats and Republicans. His decision could come "as late as after Thanksgiving," Canney said. 

That doesn't mean Republicans are holding out much hope that King will caucus with them. In fact, the GOP came to the conclusion that King almost certainly wouldn't ally himself with them months ago. The National Republican Senatorial Committee, under the leadership of Sen. John Cornyn (R-Texas), spent a considerable sum of money on attack ads against King. So did the conservative non-profit group Crossroads GPS. If King joins the Republican conference, he'll be joining the team that tried to defeat him in the campaign. 

National Democrats, meanwhile, ignored their party's Senate nominee in Maine, wagering that King would win and join them. The Democratic Senatorial Campaign Committee even provided King with cover in the form of an ad hitting Republican nominee Charlie Summers. 

"[King] talked a lot about bipartisanship and looking beyond the party label. Well, the Democrats did that this cycle [with regard to his race]," said Dennis Bailey, an aide to King during his gubernatorial tenure. Bailey thinks that King will caucus with the Democratic Party in the Senate.  "I have always thought that and I don't see anything that would change it," he said. 

Indeed, Republicans appear to be doing little to alter an outcome most strategists privately predicted months ago. The Associated Press reported that King, who arrived in Washington on Sunday, was being courted by Senate Majority Leader Harry Reid (Nev.), but that Republican leadership was not making a similar effort. Canney said it was her understanding that Republican GOP Conference Vice Chairman Roy Blunt (Mo.) had reached out to King, but that as of early Monday morning, Senate Minority Leader Mitch McConnell (Ky.) had not. 

With Democrats in the majority, there is even more incentive for King to join them. For much of the 2012 campaign, it looked like Republicans stood a chance of seizing back control of the Senate. But the GOP's dismal record on Tuesday ensured that Democrats would retain their power for at least another two years.

As a result, Reid's pitch to King -- plum committee assignments etc. -- is easier. It would be a bit more difficult to convince someone to join the side that had just lost its power. 

Even if King caucuses with the Democrats, those close to him caution that it doesn't mean he won't buck them when he disagrees. 

"I think that any notion that his vote for one or the other as a leader is going to signal some kind of blind loyalty to one party or the other is just plain wrong," said Eliot Cutler, the 2010 independent candidate for governor who was one of King's Senate campaign chairs. 

King said something similar last week. 

"I ran on the platform of trying to call them as I see them, not be locked into a party position one way or the other," he told CNN. "But on the other hand, it isn't a stunt - I'm not going down there just to plant the flag and not get anything done."

Fair enough. But, when King announces his plan to caucus with Democrats, it will be Washington's worst-kept secret.