The five primaries held Tuesday are the first since Rick Santorum suspended his presidential campaign two weeks ago, essentially conceding the GOP nomination to Romney.
Romney is still about 400 delegates short of the number he needs to formally gain his party's presidential nomination this summer at the Republican National Convention in Tampa, Fla. There are 209 delegates at stake in Tuesday's five primaries and they are generally awarded on a proportional basis.
Newt Gingrich had campaigned heavily in Delaware, hoping for a win there. Pennsylvania is also a notable win for Romney, because it is Santorum's home state.