Rick Klein of ABC News writes:

The House landscape, when combined with President Obama’s drop in popularity among critical independent voters, has the president’s fellow Democrats in a defensive mode, even as the president himself begins to go on offense on the campaign trail. That means extreme skepticism in the rank-and-file as Congress reconvenes this week for what’s likely to be the last major legislative push before campaigning subsumes policy-making.

It’s not simply that there are more than enough seats to flip control of the House and maybe of the Senate as well; it is that Democrats must now traverse a political landscape in which Obama and his agenda threaten their viability. As Klein notes:

As Democrats consult their lists of vulnerable seats, the agenda isn’t likely to help them much.Energy and immigration reform cut more along geographic boundaries than party lines. Moderate and conservative Democrats — including many vulnerable House members in the West and South — are among those who are least anxious to see action on hot-button policy issues, and are particularly concerned about runaway government spending.

If Republicans win big in November, it may not mean the end of the Obama presidency (we certainly have learned that two years in politics is forever) but it will end his aura of political invincibility. Those Democrats who survive will need to chart their own course. And internationally, friends and foes will begin to calculate and calibrate their behavior, knowing Obama may be a one-term president.