The point is that Obama is not facing a GOP Congress. Nor can the Democrats show that the GOP in the House has done anything to halt their legislative program of big spending. The rollbacks in Congress have been that the Democrats have been backing away from Obamacare until after the November elections, as everyone knows.
Furthermore, Democrats are retiring on a massive level as they realize that big government has been an economic disaster.
Obama has caused a massive recession and the Democrats need to stand up and take responsibility for what they have done. Instead, Obama has said that racism is the basis for the opposition to him--not the economy.
There is no comparison between the 1948 opposition to 16 years of Democrat total power to the current GOP opposition to the Obama economic policies that have led to high unemployment, a declining middle class, massive federal debt, widespread corruption in federal administration, stagnant incomes, and loss of health insurance coverage for millions of people.
Truman won in 1948 but his disputes with organized labor and his foreign policy problems led to the Republican landslides of 1952 and 1956.
Obama's economic disaster and the Democrat revolt over his foreign policy should lead to a GOP landslide in November, but we can't underestimate the GOP's innate ability to snatch defeat from the jaws of victory.