On the Democratic side, Hillary Clinton has led her party's primary by a lot pretty consistently. Until, that is, a new poll from CBS and the New York Times putting her lead in single digits nationally. Notice that little pincer at the end of this graph; that's mostly the CBS/Times poll weighing in.
National polling doesn't mean a lot in a contest that is composed of a series of staggered state-by-state battles. It does, however, give a broad sense of the mood of the country. And that mood, as of this week?
Donald Trump's a bigger frontrunner than Hillary Clinton. By a lot.
Hillary Clinton is also running against, essentially, one person. (Sorry Martin O'Malley!) Trump is running against something like 200, all of whom are splintering the opposition to him. But that works both ways: He's also cobbled together a third of the vote despite having so many opponents.
This does not mean that Donald Trump is a stronger general election candidate than Hillary Clinton. It does not mean that he will be the nominee and Clinton won't. What it means is that if you're going to refer to anyone as the front-runner in any race at this point, you might want to stamp that label on the guy who's never held office before.