At FiveThirtyEight, Nate Silver explains why Mitt Romney is making a last-minute play for Pennsylvania: absent Ohio, it’s basically his sole remaining (plausible) route to at least 269 electoral votes.
In a nutshell, here’s how Romney, according to Silver, gets to at least 269 EVs absent Ohio: he holds North Carolina; he wins the two toss-up states of Virginia and Florida; he wins either Colorado or New Hampshire; he wins Pennsylvania (20 EVs).
That’s it. Winning Wisconsin (10 EVs) won’t do it for Romney (that only gets him to 263 EVs). Iowa won’t do it (that gets him to just 259 EVs). He needs a big steal from the Obama-lean column. He needs Pennsylvania.
Mr. Obama is at about 50 percent of the vote in the polling average in Pennsylvania, Wisconsin, Nevada and Michigan; at close to 49 percent in Ohio; and at about 48 percent in Iowa, New Hampshire, Virginia and Colorado.
There are not really any recent precedents in which a candidate has led by something like 49 percent to 46 percent in the final polling average, as Mr. Obama does now in Ohio, and has wound up losing the state. […]
That brings us to Pennsylvania — where the forecast model puts Mr. Obama’s chances at better than 95 percent. […]
That is probably a reasonable strategy, even though Mr. Romney’s chances of pulling out a victory in Pennsylvania are slim. What makes it reasonable is that Mr. Romney’s alternative paths to an Electoral College victory are not looking all that much stronger.
Wisconsin, for instance, is one of the states where Mr. Obama has shown the sharpest rebound in his polling. Another issue for Mr. Romney is that Wisconsin allows voters to register on Election Day, which may make it one case where the likely voter models that pollsters apply are too restrictive. Polls put out by two Wisconsin-based universities, St. Norbert College and Marquette University, show a larger lead for Mr. Obama than those produced by national polling firms, which may not account for these nuances. (Democrats slightly outperformed the polling average in Wisconsin in both 2004 and 2008.)
So, in pursuing Pennsylvania, Romney is basically throwing a Hail Mary pass. Word is that the Democrats are sending Bill Clinton to the state on Monday to play the role of Randy Moss for the interception.