A 7% national popular vote victory is a landslide in contemporary American politics. Democrats showed this in 2006 when they took back the House of Representatives with a 6.49% victory. President Barack Obama again made this point in 2008, when he defeated Senator John McCain by 7.27%. Just eleven weeks ago Republicans provided a third example when they won the national popular vote for Congress by 6.83%. A 7% victory isn’t just a win--it’s a thumping, a shellacking, or some such catch-phrase.

That’s why it’s worth noting that, in the mere 75 days since the 2010 elections, Democrats have gained 7% on Republicans nationally. In so doing, they have already erased the Republican advantage ahead of the 2012 elections.

Here are two graphs of the trend in President Obama’s job approval ratings since November 2nd, both from Pollster.com. The first includes polls from Rasmussen Reports, while the second does not. Neither graph includes Zogby polls that were taken online:

President Obama Job Approval, November 2nd through current

With Rasmussen

Without Rasmussen

In both graphs, President Obama has gained a net of eight points in his job approval since November 2nd. This is a statistically significant gain that cannot be dismissed as random noise. It is also of great electoral importance for all candidates who will be running for federal office in 2012, as there is a high correlation between President Obama’s job approval and congressional vote. Here are the 2010 exit polls by Presidential job approval:

2010 congressional vote, by Presidential job approval

According to these crosstabs, a 1.0% gain in President Obama’s job approval among the electoral would translate into roughly a 0.7% gain for Democrats in the national congressional vote (and vice-versa for a decline in his approval rating). As such, an 8% gain in Presidential Obama’s job approval translates into a minimum 5% gain for Democrats in the congressional vote (see note below). Such a swing is almost enough to cancel out the entire 2010 Republican advantage on its own.

The age gap makes up the rest of the ground for Democrats. Since 2004, an enormous generational gap has appeared in American electoral politics, with younger voters strongly favoring Democrats and seniors strongly favoring Republicans. This gap causes real problems from Democrats in midterm elections, given that voters under the age of 30 disproportionately decide not to participate in midterm elections:

Long-term data from the census bureau indicates that the turnout gap between Americans above and below the age of 45 widens significantly in mid-term elections. For example, over the last nine Presidential elections, Americans aged 45-64 turned out, on average, at a rate 12.7% higher than Americans aged 25-44. However, in mid-term elections, the average gap over the last nine cycles has been 17.1%.

With the age gap in partisan voter preference just getting wider and wider, these long-term voting patterns translate into a net 2% drop for Democrats in the national popular vote margin from Presidential elections to midterm elections. Voter turnout expert Michael McDonald:

In 2010 the age gap was 16 percentage points, the largest on record. Now, because the youth tend to vote at low rates in midterm elections, this is a part of the Republican success in the 2010 election. It would be foolish to think that they will stay home in 2012. If we hypothetically apply support for Democratic House candidates in the 2010 election among various ages to the age distribution of the 2008 electorate, Democratic candidates would have received one percentage point more of the total vote.

In addition to that 1% Democratic gain, Republicans candidates in the midterm elections would have lost one percentage point on average. This makes for an average net Democratic gain of 2% in the national vote margin if the 2010 elections had been a Presidential, rather than a midterm elections.

Barring some sort of shock change in turnout patterns or partisan voter preference by age, in 2012 Democrats will get that 2% back. Combine that with the 5% net gain by Democrats from President Obama’s improving approval ratings, and the 7% national advantage Republicans used to capture the House in 2010 is already gone.

A 7% advantage is all it takes to win a national landslide in American politics, and 7% swings can happen pretty quickly. In the 75 days since the 2010 elections, we have already seen one such swing. It won’t be the last one to occur before the 2012 elections, either. The American electorate to proving to be a lot more volatile than many electoral observers, including myself, had thought after we all saw four the razor-thin elections from 1998-2004.

Note: There is not a direct, linear relationship between the Presidential job approval and congressional vote preference. The further President Obama’s approval deviates from 50%, the less of an impact further changes in his approval rating will have on the national congressional vote. However, since his approval rating remains close to 50%, and since there are very few generic congressional ballots at this time (don’t trust Rasmussen), it is reasonably safe to assume a strong correlation between Presidential approval and congressional vote preference.