Oh I think Pennsylvania will surprise a lot of people in the next decade and move to the right. It might become the new Virginia as in where Virginia was before.
The last Republican to carry Pennsylvania in a Democratic election-victory year dates back to 1948. Since after the 1940s, Pennsylvania has produced margins with Democratic tilts. Republican winners having carried the Keystone State—Dwight Eisenhower (1952, 1956), Richard Nixon (1972), Ronald Reagan (1980, 1984), and George Bush (1988)—all underperformed statewide-vs-nationwide. Losing Democrats Hubert Humphrey (1968), Al Gore (2000), and John Kerry (2004) had Pennsylvania in their column despite those Republican election-victory years. And, since after the 1940s, all prevailing Democrats—John Kennedy (1960), Lyndon Johnson (1964), Jimmy Carter (1976), Bill Ciinton (1992, 1996), and Barack Obama (2008, 2012)—carried Pennsylvania by larger margins compared to their national numbers.
Pennsylvania is a base state for the Democratic party. I know that the 44th president carried by less than 2 points above his national number with Election 2012. But that was also the case with the 42nd president with his re-election from 1996.
You have to make a
connection, long term, with a host of states from a given column and another host of states from another given column and, yet, another host of states from yet another given column…. States which have, historically and electorally, carried the same for much of their existence. Pennsylvania is connected with Michigan. With Mich. the younger of the two, there are five presidential elections of record for which these two states carried differently. Three of those were cycles in which either Pa. or Mich. had a major-party nominee who didn't carry the other state. (Those were in 1848, 1856, and 1976.) And the other two were in line with having carried for Franklin Roosevelt in three of his four elections. (Roosevelt's Democratic party's base states were not in the north, as is the case now, but in the south. FDR failed to flip Pa. as he unseated Republican Herbert Hoover in 1932, and the Keystone State was one of six states to hold for Hoover, and Mich. flipped for losing GOP opponent Wendell Wilkie in 1940.)
States which have historically voted the same as the duo Pennsylvania/Michigan include New Englander Connecticut. (It has voted the same as Mich.—with no broken streak—since 1948. Obviously Pa. disagreed in 1976.) After that, you can have fun with so many others with a common connection. Like New Jersey. Like Maryland. Like Illinois. Like … .
Pennsylvania may become won over by a prevailing Republican presidential candidate only if that elected GOP performs nationally by a margin large enough to pull in a limited number of states which do not default, as the base, to Team Red. (For that happen, Pa. wouldn't be the only one in its group to cross the aisle, so to speak.) And this period's Republican party—with their base states in the south—hasn't won the U.S. Popular Vote more than once since after the 1980s. Add to this the fact the female vote hasn't nationally been carried by a GOP in any given election following the 1980s. In 1988, George Bush won nationally (R+7.73) over Michael Dukakis, and he was the last prevailing Republican to carry the state of Pennsylvania (by R+2.31).
