Right now Donald Trump is down in the polls, with his remarks about the judge on his Trump University case reverberating and Hillary Clinton getting a bounce from having finally captured the Dem nomination (I know, I know, Bernie still has a chance if she gets indicted before the convention, but... ). But it was just quite recently that they were nearly even in the polls, and that condition could return. Nobody should forget that at this time in 1980, Jimmy Carter had a double digit lead in the polls over Ronald Reagan and Dems were just salivating at the chance to run against that "extremist." But, well, heck, there we go again.
So the problem is that it looks like the US may be weakening. Last month's job report was simply dismal, and most are writing it off as a one month wonder. I hope so. But there have also been reports that the US job market has been weakening since January. We may be on a trend here that may be hard to reverse.
Janet Yellen has been still talking up interest rate increases, but even she recognizes "four uncertainties," and a concatenation of more than one of these could easily tip a weakening and fragile world economy downwards even into a recession, possibly with a market crash this fall. The obvious near term shock could be positive Brexit vote, and while I think some have exaggerated the near term badness of this for the UK economy, even a small shock at the wrong time can push things over, as old chaos theorist me knows all too well, and we may have such a fragile situation.
Once things get going down this can easily spread. Parts of Latin America, especially Brazil, are not doing well. Europe has interest rates as low as they can go pretty much, even though all of the EU except Greece currently has positive GDP growth. Concerns about China have retreated somewhat, but its property market remains way overvalued, and its growth has decelerated. All this is fragile. And one of the uncertainties is oil, where a shock of one sort or another could show up with little warning.
In short, the probability of the US economy actually going into a decline prior to the November election is higher than many think, I think. All it probably takes is a couple of those uncertainties hitting, and the Fed is pretty limited in what it can do in the short term, and, of course, there will be no fiscal policy stimulus. Heck, the Republicans in Congress would welcome such an event, given its likely political result.
Throw on top of this the non-trivial possibility that terrorist groups will make a major attack shortly before the election in an effort to get Trump elected (having an overtly Muslim-hating US president would be great for their recruiting), and, well, I shall be holding my breath all the way, whatever others may be doing.