The story of centrist Democratic opposition to President Obama's budget, which began to trickle into view this morning, will unfold gradually over this month and next. Democrats won't be fully challenged to embrace Obama's vision for a remodeling of tax and health care policy until April, when the full details of the White House budget emerge.

Congress will then craft its own budget blueprint, taking some cues from Obama but potentially abandoning some of the White House's proposals. The 28% taxation limit on itemized deductions is already taking bipartisan fire and looks like a good bet to be jettisoned, despite uncertain evidence that it would have a negative effect on charitable giving.

So we know already that more than a dozen centrist Dems are meeting to weigh their concerns about the White House budget, while Republicans lick their chops in glee at the brewing rebellion.

But what about the three GOPers whose votes helped put the stimulus bill over the top? In their responses to the budget last week, Sens. Arlen Specter (PA), Olympia Snowe (ME), and Susan Collins (ME) offered one palpable clue about their opinion ...

... that they won't reveal it until the full Obama budget comes out in April. From Specter's statement:

It is impossible to evaluate adequately the President's ten-year budget until the release of the full documents.

Here's how Collins put it:

I will closely examine the full budget proposal when the details become available in the coming weeks.

Snowe was less direct in her response to the budget, remarking that the budget outline was "bold with its intention" but "scarce on details." Still, don't look for these three to get out too far in front of the budget this month -- despite Snowe and Specter's admirable climate change advocacy. They're likely to be watching how centrist Democratic critics air their grievances before making their opinions known.

But keep in mind that the budget will be immune to a filibuster, meaning that Democrats can afford to lose eight of their own members (assuming the Minnesota race remains unresolved) without the need to gain a GOP vote.