Who is politically vulnerable if 2008 turns out to be a recession year? That question is harder to answer today than it was in 2006 and for several years before that because Republicans then controlled the executive and legislative branches of government.

It was frequently pointed out after President Bush’s 2004 election victory that he and the GOP would own any boom or bust; there was talk, less convincing then than now, that the economy was in trouble.

But the political picture is now fuzzier. Although Bush is still ensconced in the White House and presidents generally get credit or blame for the condition of the economy, Democrats have run both the House and Senate for a year, and it is Congress that holds the purse strings.

Significantly, Bush changed his tone this week, abandoning his customary upbeat assessment of the nation’s economic prospects. He noted that people should not “take growth for granted.”

This was carefully phrased — both acknowledging the possibility of contraction and warning Democrats against adopting policies that could knock markets and economic confidence generally.

Which, according to Bush, means raising taxes and increasing government spending.

Several of the tax cuts Bush pushed through in his first term of office are due to expire by 2010 and Democrats are committed to letting them do so. The GOP wants to make the cuts permanent, but the party now in charge has no intention of obliging. Ways and Means Committee Chairman Charles Rangel’s (D-N.Y.) “mother of all tax reforms” assumes the sunsetting of cuts in taxes on capital gains and dividends, for example.

Out on the presidential campaign trail, candidates are finding that economic issues have replaced the Iraq war as the leading cause of concern among voters. Thousands upon thousands of people have lost the homes they bought at too high a price and too high a mortgage rate. The sub-prime crisis is rippling through sector after sector.

Speaker Nancy Pelosi (D-Calif.) is mulling whether she should press forward with an economic stimulus package to avoid recession. Her caucus chairman, Rep. Rahm Emanuel (D-Ill.), suggested to The New York Times on Monday that the battle between Congress and the administration would be over whether such a package should include broad tax cuts or be targeted more narrowly at the middle class and the poor.

Argument appears to be focused not on whether there should be action at the federal level to ameliorate the malign effects of a downturn, but how it should be done, and how soon.

Both sides are, naturally, readying to play the blame game on an unattractive economic landscape. It won’t be pretty.