If anyone wonders why Democrats seem dispirited in 2010, CBS uses 2008 to explain it.  In their latest survey, CBS asked voters who backed Obama in 2008 whether they planned to vote for Democrats in the midterms.  Only two-thirds would commit to it, and only 42% of independents:

CBS News senior White House correspondent Bill Plante reports that, for the White House, keeping control of the House and Senate is all about getting Democrats and Independents who voted for the president in 2008 back to the polls, and on that score, the latest poll numbers show Mr. Obama hasn’t closed the sale.

Only two-thirds of Obama voters in 2008 (67 percent) say they’ll vote for one of his fellow Democrats in 2010. Eight percent of those voters say they will vote Republican this year, and 21 percent say it depends.

The biggest erosion of support is among independents; just 42 percent of Obama’s 2008 independent voters say they’ll support a Democrat this year. Twelve percent say they’ll vote for a Republican, and 38 percent were still undecided.

By the way, these are 2008 Obama voters who are likely to vote this year, not the larger sample of all 2008 Obama voters.  The overall survey polled 1077 2008 Obama voters, but CBS doesn’t say how many of those turned out to be likely to vote in this year’s midterms.  Also, this was an online survey (not the same thing as a website poll), which is generally considered somewhat less reliable than phone surveys.

Even with those caveats, the breakouts are intriguing, especially among independents.  No Republicans who crossed party lines in 2008 were apparently included in this survey, but the unaffiliated voters show just how much ground Obama has lost.  Twelve percent of indie Obama voters in 2008 are committed to voting Republican in the midterms, and 38% are still mulling that option.  Potentially losing 58% of the independents that backed Obama is a disaster, especially added to independents overall who are likely to vote in this cycle.

Why are they leaving?  A near-majority of independent Obama voters declare themselves “dissatisfied” with Washington after two years of full Democratic control, and another 20% describe themselves as “angry.”  None declare themselves “enthusiastic,” and only 30% “satisfied.”  Those are not turnout numbers.  If Democrats are lucky, the 69% who are dissatisfied or angry will just stay home, but it’s a pretty sure bet that some of them will be voting Republican.

Nor is that the only problem on that question.  Among Democrats who voted for Obama, 43% pronounce themselves “dissatisfied” and another 10% “angry” about Washington in the Hopenchange era.  Those also indicate a turnout problem in two weeks for Democrats.

On Obama himself, the pool of likely 2008 Obama voters give him an approval rating of 82/18, which sounds great, except that it shows an erosion among Obama’s base, not just in the general electorate.  They don’t give Obama or Democrats much credit for “change” either; only 16% think Obama has brought “a lot” of change, with 51% saying “some” and 32% not much or none at all.  Those numbers go to 9/43/48 among independents.

Disillusion is a powerful force in politics, and if this survey is at all accurate, we will be able to measure that force in two weeks.