The White House's "full support." The backing of Senate leadership. The promise to retain his rank. Pennsylvania Sen. Arlen Specter appeared to gain a new political world for leaving the party that brought him to national politics. One week later, that world is gone.

Specter now stands alone. Stripped of his rank by Democrats. Scorned by Republicans. Specter's flash of strength has turned to weakness.

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That weakness was thrown into stark relief Wednesday night, as Rep. Joe Sestak said in an interview that he was "very seriously" considering challenging Specter in the Democratic primary. There was a renewed energy to Sestak, repeating the phrase "very seriously" as he drove from Washington DC to Pittsburgh.

It was only last week that Sestak appeared blindsided. "You know," Sestak told MSNBC's Chris Matthews Friday with a pang of resignation, "I was thinking of getting in. And I haven't made my final decision."

How quickly the winds have changed.

Barack Obama was handed a political gift on his 100th day in office. A moderate Republican came to the White House to offer his Democratic allegiance and potentially an invincible legislative majority. Obama and Vice President Joe Biden received Specter publicly, courting live coverage on the cable networks. It was a celebration.

President Obama told Specter he would campaign for him. Obama offered his "full support," a pledge reiterated by top White House officials.

Specter was to be no "rubber stamp." But the exchange was implicit. On some big bills, perhaps health care, Specter could offer the scale-tipping 60th vote. Obama would avoid contentious procedural maneuvers. In return, Specter was to keep his veteran status and win the mighty Democratic leadership’s favor.

Senate Majority Leader Harry Reid put it plainly to National Journal reporters on Friday. Specter, Reid said, "will maintain his overall seniority in the Senate and it's pretty clear that he's going to do that."

Specter repaid that assurance by testing Democrats' patience. In his first week as a Democrat, Specter voted against the Democratic budget. He also opposed a bill, which was defeated, that would have granted homeowners in financial distress more flexibility to renegotiate their mortgage.

By Sunday, on NBC's "Meet the Press," Specter was asked about Reid's assurance. "That's an entitlement. I've earned the seniority," Specter said. "I will be treated by the Democrats as if I'd been elected as a Democrat."

The "entitlement" notion did not sit well within the Democratic caucus. Specter was a fair-weather partisan, in some Democrats' view. He left Democrats at the dusk of their last majority in the 1960s. Here he was returning at dawn.

Soon even that allegiance came into question. This week Specter told the New York Times that Republican Norm Coleman should be seated over his Democratic opponent Al Franken, in Minnesota's still disputed Senate race.

"Arlen," Reid asked Specter on the Senate floor. "What's going on here?"

"I forgot what team I was on," Specter replied.

Specter tried to retract the statement. But the damage was done. No Democrats were excited to step aside and offer Specter a key place in the Senate committee pecking order. Specter gave opponents reason to reject him.

Tuesday night, the Senate voted to strip Specter of his seniority. Specter has served in the Senate for twenty-nine years. The vote left him with the power of a freshman.

Specter responded Wednesday morning with a written statement, again noting Reid's promise that "I would have the same seniority as if I had been elected as a Democrat in 1980."

Reid remains optimistic. He told CNN that, "we can try to work something out with individual chairmen."

Specter may get a subcommittee chairmanship in the Judiciary arena. Someone may step aside. Some consolation prize is likely. But hard feelings will linger. For Democrats and Specter, this is not how the story was supposed to go.

Specter is now a man without a country. His old side views him as a traitor. His new side is skeptical of the longtime adversary turned ally. The episode has left him politically weakened and embarrassed.

The president and the majority leader are chastised as well. Barack Obama talked like Lyndon Johnson as he backed Specter, only for Democratic senators to revolt and leave this president painted as no master of the Senate. Reid appears weaker for failing to deliver the political spoils he promised his recruit.

Even liberal bête noire Joe Lieberman escaped the Specter treatment. Lieberman sided with Republicans on the most controversial issue of the Bush era, the war in Iraq. He vocally backed Republican John McCain in the 2008 campaign. Yet Lieberman kept his seniority.

Today, Specter has gone from ranking Republican to the lowest Democrat on the Judiciary Committee. Poignantly, Specter will be the last senator to interview Obama's first Supreme Court nominee.

And what of that 60th vote? Specter, as the moderate Republican, faced pressure to vote somewhat with the GOP to prove his loyalty. As a Democrat, that pressure was to be reversed.

But Democrats have humiliated Specter. Specter could respond by withholding the 60th vote on the key legislation. Obama never would have agreed to Specter's switch if the president had not viewed some bills as urgent. After all, a new Democrat could have come in 2010.

That's the irony of Specter. Specter's defection was, he admitted, rooted in political survival. Republicans had turned against him. He could not win a GOP primary. Now, in moving to Democrats to survive, Democrats have turned against Specter.

Enter Sestak, the second-term Pennsylvania House member and retired Navy vice-admiral. To Sestak, Democrats decision to strip Specter of his seniority "solidifies how I felt when I heard what the Washington establishment had done.

"The Washington Democratic leadership does not speak for all Democrats," Sestak continued. "This is not a place of king or king makers and it looks like the Democratic senators felt the same way."

Indeed, in Specter's case, Obama and Reid proved no party kings.

By Wednesday night, Specter's likely challenger was attending a Jefferson-Jackson dinner to court Democrats. And the candidate Obama and Reid backed appeared blindsided. Specter decided to cancel his scheduled appearance Wednesday evening on CNN's "Larry King Live."

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