Joe Biden, Ronald Reagan.

Doyle McManus, Tribune News Service

Joe Biden took another step toward locking up the Democratic nomination. His lead in delegates has begun to look insurmountable. But now the presidential race enters uncharted territory due to the coronavirus crisis. Tuesday’s three primaries may be the last large campaign gatherings for a month or more; at least five other states are postponing their primaries.

The normal rituals of a campaign — giant rallies, town meetings, barnstorming tours — have been cancelled. The Democratic and Republican political conventions, scheduled for July and August, may be next.

So what should Biden do? Here’s my advice.

Be presidential: Biden is best when he contrasts himself with President Donald Trump. His strong suit is his eight years as President Barack Obama’s vice president — but he has to answer for old votes from his 36 years in the Senate before that.

His strongest moment in his one-on-one debate with Bernie Sanders on Sunday was his crisp answer on how he would address the coronavirus crisis as president. “First of all, I have to take care of those who, in fact, are exposed or likely to be exposed to the virus, and that means we have to do testing,” he said. “Secondly, I would make sure that every state in the union had at least 10 places where they had drive-thru testing arrangements. I would also, at this point, deal with the need to begin to plan for the need for additional hospital beds.... But we have to deal with the economic fallout quickly, and that means making sure the people who in fact lose their job, don’t get a paycheck, can’t pay their mortgage, are able to pay it.”

David Axelrod, Obama’s former political strategist, has often been critical of Biden’s campaign, but he pronounced that answer “sensational.”

“He sounded like a guy who knew how to handle it,” Axelrod said.

Reach out to Sanders and his voters: The race for the nomination isn’t over unless Sanders drops out. The Vermont senator has every right to compete for votes, especially with primaries on hold in New York, Ohio, Georgia and other states.

But that shouldn’t stop Biden and Sanders from reconciling. In Sunday’s debate, Sanders was uncharacteristically restrained in his critiques of Biden’s positions. At one point, he even said Biden’s “heart is in the right place.”

Biden, on the other hand, criticized Sanders’ “Medicare for All” health care plan and pointed out that a single-payer system in Italy hasn’t coped well with the coronavirus epidemic. He might have been better served by emphasizing what he and Sanders have in common — a commitment to universal health care, for example. Even without rallies, a candidate can make news: In Sunday’s debate, Biden grabbed headlines by promising to choose a woman as his running mate.

Finally, get plenty of rest.

This year’s campaign has produced the mystery of the two Joe Bidens.

He’s long been a gaffe machine, prone to stumble over his words or make an impolitic remark. He’s been especially tongue-tied in debates with lots of candidates shouting to be heard — but there won’t be any more of those.

At 77, he’s undeniably lost a step from the Biden who first ran for president in 1988 or for vice president in 2008. But claims by President Trump and his supporters that Biden suffers from some form of dementia are malicious and don’t stand up.

And any voter who watches a highlight reel of Biden’s flubs should compare it to Trump’s stumbles and lies, which are at least as alarming — and the president is only 73.

Still, any candidate in his 70s should know his limits. In 1984, President Ronald Reagan, then 73, trimmed his reelection campaign appearances to one a day, and mostly read set-piece speeches. Reagan won 49 states.