"The killer calculus of President Obama’s re-election" is the subject of the sentence?

How likely it is that he'll be re-elected.

To begin with, that's not really a sentence. That's a summary of what the opinion piece will be about.

Secondarily, "re-election chances" belongs together. You've broken a phrase up with your underlining.

In his opinion piece, Mr. Silver is going to try to tell you how he assesses Mr. Obama's likelihood of being re-elected. The factors he will look at in his assessment/equation include Mr. Obama's current approval rating, the projected growth of the U.S. GDP in 2012, and the political ideology of whoever the Republican nominee will be.

Excellent.
Thanks.
PS, does "killer calculus" mean "key calculation?"

Calling something a "killer" top of the line, over the top.

"She made a killer pizza the other night."

"He drives a killer car.'

"killer calculus" = ultimate formula

Cool.