The polls are not closed yet and excuses are already being offered for the expected Democratic losses. My favorite, so far, is one from CBS News - Democrats' Problems in 2010 Started with 2008's Economic Collapse but I have to review some recent history to explain why.
Typically in a presidential election year, the Democrat leads the polls through the Summer, cresting with the Democratic convention. The Republican pulls ahead after their convention. After that the real race begins - will the Republican keep his lead or will it decline as soon as the convention ends? This does not include blow-out years where the challenger never had a chance against the incumbent but it does describe the 1980, 1988, 1992, 2000, and 2004 races.
2008 seemed to be following the same pattern. Remember, Barack Obama did not outright win the primaries. Hillary Clinton won a lot of delegates before running out of money and she continued to win delegates through the last primary. It was only after she conceded that Obama had enough delegates to guarantee the nomination.
Another factor is that the candidate who sews up the nomination first usually wins. This is because that candidate has a united party behind him. McCain won the nomination months before Obama did and there was some fear that spurned women voters would flock to the Republicans, especially with a woman on the ballot.
During the Summer Obama was ahead in the polls but not by much. His lead was often smaller than the margin of error. Many analysis suspected that McCain was actually ahead but that respondents were afraid of sounding racist by telling pollsters that they were going to vote for McCain.
After the conventions, McCain was ahead in the polls.
So what happened? How did Obama go from long-shot to inevitable?
The economy crashed.
McCain suspended his campaign for a week for an emergency trip to DC. This might have paid off if McCain had followed up and criticized Obama for not doing the same thing and putting country first. He did not.
The crash hurt the Republicans. The response - multiple bailouts and the TARP also hurt the Republicans (even though the Congressional Republicans were against the TARP, Bush was for it and his party suffered by association).
That is when Obama took the lead in the polls and maintained it through the election. And that is why blaming the Democrats' problems on the 2008 crash is so ironic. If it wasn't for the crash the Democrats might never have taken the White House. They were elected to fix the economy.
Their response after the 2008 election hurt them more. Conservatives wanted to see poorly-managed banks fail. Liberals wanted either a bank take-over or prosecution of bankers. neither happened. Instead we got more bailouts. The country wanted to see an end to earmarks. Instead the stimulus was seen as the Mother of All Pork. The country's top priority was the economy but the Democrats couldn't talk about anything except health care. Even then, people wanted real health care reform. Instead they got a wonky bill that still has experts trying to decide what it will cover. The headline for the weekend was that the health care bill may (or may not) include free birth control. I doubt that most voters are aware of the financial reform bill that the Democrats passed and that even fewer know what is in it.
The Democrats had their chance. They were elected to fix the economy. They also promised to win the war in Afghanistan, get the troops out of Iraq, close Gitmo, repeal the Patriot Act and end Don't Ask Don't Tell. They failed on all of these. If they had managed a better recovery then the country would forgive them all of their other lapses but unemployment is stuck at 9.5% and the don't have a clue what to about it.
So, it would be more accurate to describe the 2008 as a missed opportunity rather than a problem.