Suppose that Obama's voters had turned out in 2010 to vote for down ballot offices in as large numbers as they turned out in 2008. Where would the US economy be now?
There would have been no tea party Republican Governors' slashing of state employment, with attendance multiplier effect putting downward pressure on there and neighboring economies. There would have been no debt ceiling crisis to add substantially to economic uncertainty and increase the flight to quality. There would have been Larry Summers infrastructure bank, which would now be pumping out $200 billion a year in badly needed infrastructure investment.
Add all those up, and you get on economy with between $300 billion and $600 billion more of annual spending, depending on the multiplier. That is an economy with unemployment rate in the low 7s or the 6 percents. That's an economy growing at 3 to 4% per year instead of 1 to 2% per year. That some economy with a lower projected deficits and debt to GDP ratio then the economy we have today.
The failure of marginal Obama 2008 voters to turn out for down ballot candidates in 2010 was a disaster for America.
The election of Mitt Romney and a supporting congress this November would be a much bigger disaster for America. Think of the trainwreck that has been the Conservative government in Britain since 2010. And square it.