Joe Biden is on track for another big win in the primaries — but will it be big enough to end them?

While the world is gripped by the latest developments in the COVID-19 pandemic, the wheels of American democracy keep turning — four big states head to the polls Tuesday for the Democratic primaries. The results appear likely to heavily favour former vice-president Joe Biden over Sen. Bernie Sanders.

They could make Biden's eventual triumph all but inevitable.

Even before Tuesday's voting began, Biden was in an enviable position. According to estimates from the Associated Press on Monday afternoon, Biden had 894 pledged delegates against 743 for Sanders. While that might seem like a relatively slim margin, the number of delegates still up for grabs is quickly shrinking — and with them, Sanders's hopes for turning his campaign around.

Just under half of the 3,979 pledged delegates heading to the Democratic National Convention in July already have been awarded. Florida, Illinois, Ohio and Arizona — the four states voting on Tuesday — will bring that proportion up to 61 per cent.

And they're likely to build on Biden's lead.

Biden doing better than Clinton did

Last Tuesday, Biden beat Sanders in the Michigan, Missouri, Mississippi and Idaho primaries, while Sanders prevailed only in the North Dakota caucuses. Washington is, at the moment, still too close to call — which itself shows you how much Sanders has struggled since the field of major candidates was winnowed down to two. In 2016, Sanders beat Hillary Clinton in Washington by a margin of 46 points.

National polls suggest Biden might be opening up a wider lead over Sanders than Clinton did in the last Democratic primary. Two polls conducted since last week's round of voting, by Morning Consult and NBC-Wall Street Journal, gave Biden a lead of 24 and 29 points, respectively. At this point in the 2016 cycle, Clinton's lead was less than half that.

Biden is putting up the same kind of dominant numbers in each of the four states voting on Tuesday.

In Florida (with 219 delegates, by far the biggest prize of the night), Biden is averaging around 63 per cent support and Sanders is trailing with 27 per cent. In Illinois, Biden is averaging 60 per cent to 31 per cent for Sanders. 

The race is looking somewhat closer in Ohio and Arizona, but Sanders still trails there by a wide margin — about 23 points in Ohio and 18 in Arizona.

Delegate math about to get even harder for Sanders

It's possible that Sunday's debate between Biden and Sanders shifted voting intentions from where the two candidates stood when these polls were conducted. One debate survey, however, suggests neither candidate gained a significant advantage. The COVID-19 outbreak also has the potential to significantly affect public opinion and turnout in unpredictable ways.

But unless Sanders is able to mount an exceptional upset on Tuesday, the nomination will be left out of reach for the Vermont senator — even more so than it might be already.

At the moment, Sanders needs to win roughly 59 per cent of all remaining delegates to emerge with a majority at the convention. Based on where the national polls stand now, that's unlikely but not impossible — assuming the last week represented a radical shift in the campaign that has not yet been picked up by the polling.

If, however, the results of Tuesday's voting are roughly in line with current polling in the four states, the numbers will start to look unachievable for even the most wide-eyed optimist.

With the kind of lead the polls are giving Biden, he could open up a margin of more than 300 delegates over Sanders. If that happens, the mark Sanders would need to meet in the remaining primaries would be 69 per cent of delegates. The race from here on out would need to be more of a landslide for Sanders than even Biden is currently enjoying — with Sanders winning by more than a two-to-one margin.

It does raise the question of just how much longer this race will continue, particularly in the context of the COVID-19 outbreak and the public health risk campaigning poses. The dramatic movement toward Biden in this primary — one of the biggest in American history — suggests voters may want this to be over.

Tuesday's results could provide a strong sign that, for all intents and purposes, it already is.