Even as early returns showed Hillary Clinton with an enormous lead over Bernie Sanders in Ohio's Democratic primary, campaign workers and volunteers gathered at a downtown Cleveland bar were reluctant to start celebrating.

This election had already brought too many bizarre twists and turns, and too many examples of establishment candidates being stunned by populist outsiders, for them to take anything for granted.

However, about 45 minutes after the polls had closed, as television networks began to call the race for their candidate, they were able to relax a little – hugging and chanting their candidate's name in a way that suggested relief, as much as excitement, that their candidate had finally turned this nomination campaign decisively in her favour.

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Handily winning Florida and North Carolina on top of Ohio, Ms. Clinton won enough delegates to all but guarantee her the Democratic nomination. But perhaps more important than that, since she would have retained a strong delegate lead even if Mr. Sanders edged her in Ohio and a couple of other states, is that she thwarted a potential narrative that she's too weak in the Rust Belt battlegrounds that typically pave the path to the White House.

Last week's stunning upset victory by Mr. Sanders in Michigan, where Ms. Clinton had been leading by double digits in polls, caused no shortage of alarm in the front-runner's camp and among many officials of the Democratic Party.

A similar result in Ohio would have led to a great amount of hand-wringing about her general-election viability in parts of the country where there is anger or frustration with an uneven recovery from the recession that hit the better part of a decade ago, and a strong feeling of having been left behind.

As polls showed her with a narrower lead in Ohio, there was a growing and palpable nervousness among Ms. Clinton's supporters, especially about an array of factors conspiring against her and working in Mr. Sanders's favour – some of which were familiar from Michigan.

Among those factors is large pockets of college students, who have come out in droves to both vote and volunteer for Mr. Sanders. And the democratic socialist, who has promised younger voters free tuition, seemed to be tapping into that demographic in this state as elsewhere; his rally on Monday in the northeast Ohio city of Youngstown, for instance, seemed to be attended by half the local state college's student body.

In that sort of town, as across the Rust Belt, those students threatened to mix with another group that has given Mr. Sanders momentum against Ms. Clinton: white, blue-collar voters who feel their country's economy is working against them. Particularly with union members, or those who belonged to unions before losing their traditional manufacturing jobs, Mr. Sanders's anti-free-trade message has seemed to resonate on the Democratic side as Donald Trump's has with Republicans – leading to obvious questions about whom they would side with in a contest between Mr. Trump and Ms. Clinton.

Even African-Americans, who have powered Ms. Clinton to big wins over Mr. Sanders in southern states, seemed to be a little less reliably in her camp than previously. That was more of a concern in Illinois (Ms. Clinton held a narrow lead in that state Tuesday night), where negative association with Chicago Mayor Rahm Emmanuel – under heavy criticism for his response to a killing by police – stood to hurt Ms. Clinton. But in a city such as Cleveland, it was not hard to find African-American supporters who said they had recently gone to Mr. Sanders's camp. (One such woman could be spotted outside his local field office on Tuesday, having seemingly taken it upon herself to implore passing motorists to get to the polls.)

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And then there was another group that emerged in the runup to Ohio's vote: registered Democrats who took advantage of their state's open voting rules to cast ballots in the Republican contest instead. Stories abounded of such voters on Tuesday, and numbers that were released through the day backed them up. Some of them were the sorts of independent-minded voters Mr. Trump has boasted of attracting to the Republican side. But more of them were pragmatic Democrats, presumably more inclined toward Ms. Clinton than Mr. Sanders, who are horrified by Mr. Trump and temporarily crossed over to help relatively moderate Ohio Governor John Kasich defeat him.

That Ms. Clinton was able to overcome all that does not necessarily mean she will face a completely smooth path from here on out. As long as Mr. Sanders stays in the race, trying if nothing else to keep his issues on the radar and keep pushing Ms. Clinton to the left, she may still have to exert some energy against him rather than focusing squarely on Mr. Trump or whomever the Republican nominee proves to be.

But any frustrations or disappointments at Mr. Sanders's hand are unlikely to be as much of a setback for her as Ohio could have been. She and her supporters can keep breathing a little easier, finally.