The bottom of the ticket follows the top of the ticket...
And that is why Republicans are so nervous. Not only might they lose the Presidency, they will not take back the Senate and they might lose the House as well.
Karl Rove, the mastermind behind the Romney campaign, must be debating whether or not to spend more money on the House races or more on the Presidential campaign? If they lose the House, which they won by historic numbers in just the last election, it would be a debacle for the Republican Party.
It would be very unusual for voters to vote for the bottom of a ticket and not vote for the top and vice-versa. If Mitt Romney continues to sink in the polls, it is very possible that the Democrats could be put in charge of government with a mandate from the people. Then the onus would fall on the Democrats to fix the problems that have stalemated our government for the last 4 years, i.e., the filibuster and the budget imbalances and the jobs shortages.
Panic is beginning to set in within the Republican loyalists. Obvious desperation can be seen in their actions and heard in their voices. They are getting ready for their "come to Jesus" moment.