Assuming that Biden is the guy, does a "Default" nominee have any chance against Trump?

"Look, having nuclear—my uncle was a great professor and scientist and engineer, Dr. John Trump at MIT; good genes, very good genes, OK, very smart, the Wharton School of Finance, very good, very smart—you know, if you’re a conservative Republican, if I were a liberal, if, like, OK, if I ran as a liberal Democrat, they would say I'm one of the smartest people anywhere in the world—it’s true!—but when you're a conservative Republican they try—oh, do they do a number—that’s why I always start off: Went to Wharton, was a good student, went there, went there, did this, built a fortune—you know I have to give my like credentials all the time, because we’re a little disadvantaged—but you look at the nuclear deal, the thing that really bothers me—it would have been so easy, and it’s not as important as these lives are (nuclear is powerful; my uncle explained that to me many, many years ago, the power and that was 35 years ago; he would explain the power of what's going to happen and he was right—who would have thought?), but when you look at what's going on with the four prisoners—now it used to be three, now it’s four—but when it was three and even now, I would have said it's all in the messenger; fellas, and it is fellas because, you know, they don't, they haven’t figured that the women are smarter right now than the men, so, you know, it’s gonna take them about another 150 years—but the Persians are great negotiators, the Iranians are great negotiators, so, and they, they just killed, they just killed us." -Donald Trump

Biden certainly has a chance. According to RealClearPolitics here is where we stand in the swing states (between Biden and Trump):

- Pennsylvania: Tied 47% each

- Michigan: Biden leads Trump 47%-43%

- Wisconsin: Tied at 47% each

- Florida: Biden leads Trump 51%-40%

- Ohio: Biden leads trump 48%-46%

- Arizona: Trump leads Biden 46.5% - 46%

One interesting state is Minnesota, which would not generally be considered a swing state (it last went to a Republican in 1972). Trump only lost it by 1.5% in 2016, though current RCP polling indicates Biden leads Trump 50%-38%.

So if current polling holds, we're looking at Democrats sitting with 312 electoral votes to the Republicans' 196 (with Wisconsin and Pennsylvania being too close to call), however, only 270 are needed to win.

Obviously it's a long time until the election, and plenty of polling falls within the margin of error.

Assuming that Biden wins.  Most likely his VP will become the president.