With President Biden’s exit from the race, Democrats are quickly coalescing around Vice President Harris. Too quickly, arguably: Both she and the country would be better served by a brief, contested nomination process that tested her skills as a presidential campaigner and sparked discussion about where the next generation of Democratic leaders should take the party.

The party seems to have made up its mind, though. So now it’s the nation’s turn. Fate has presented Ms. Harris the rarest of political opportunities: to start a presidential campaign in the summer of an election year as a fresh, all-but-anointed candidate free to present her vision to all voters, not just to her own party. Though many Americans might already have feelings about their vice president, they are listening now.

To a country that could use reassurance — indeed, to those Americans who like much of Mr. Biden’s record — Ms. Harris could start by explaining how much of a reset she would represent. A clean break from Bidenism would be a mistake.

When Ms. Harris sought the 2020 Democratic presidential nomination, she tried to play down her record as a tough-on-crime California prosecutor and embrace the progressive left of the Democratic Party, backing policies that lacked broad appeal, such as Medicare-for-all. She did not make it out of 2019 before folding her campaign. Mr. Biden prevailed, in both the primaries and the general, after declining to court the passionate minority to whom candidates such as Sen. Elizabeth Warren (D-Mass.) and Sen. Bernie Sanders (I-Vt.) appealed. Amid much activist mockery of his refusal to give up on bipartisanship or on a return to civility in politics — indeed, on the broad middle of the country — Mr. Biden built a coalition of liberals, voters of color, moderates and ex-Republicans.

In the White House, Mr. Biden’s approach helped get substantial bipartisan bills over the finish line, investing in national infrastructure and critical semiconductor manufacturing. He also signed a bill that should have been bipartisan: the nation’s most ambitious climate change policy to date.

Ms. Harris should both resist activist demands that would push her to the left and ignore the social media micro-rebellion that will follow. Ms. Harris’s pick of running mate could be a revealing early indicator, too. Tapping a politician likely to appeal to the median voter would serve her — and the country — best.

Ms. Harris appears to be showing due respect for Mr. Biden. Speaking Monday at the White House to college athletes who won national championships this school year, she signaled that she intends to run on Mr. Biden’s record. “In one term, he has already surpassed the legacy of most presidents who have served two terms,” she said. She traveled in the afternoon to Wilmington, Del., to deliver a pep talk to Biden campaign staffers, who now all work for her.

This is not to say that Mr. Biden has made no mistakes, or that Ms. Harris should run as a Biden clone. The president has sometimes tried to pander to voters with policies such as widespread student debt cancellation or, more recently, nationwide rent stabilization. Mr. Biden has generally picked smart, competent staff — but not always — and Ms. Harris could say which of them she might keep.

More to the point, Mr. Biden’s approval rating has been mired in the 30s. Majorities disapprove of the Biden administration’s handling of several issues that voters care about most, including inflation and immigration.

Ms. Harris might look at those numbers, and the complexity of the issues, and be tempted to ride a glide path to the nomination, taking few risks between now and when delegates vote in August. She should do the opposite. She could deliver a detailed national address and take substantive questions from journalists, hold a televised town hall to engage directly with voters and give interviews after rallies in battleground states. She could even take part in forums with fellow Democrats to showcase that the party is more than any one individual.

The goal is to emerge from vice-presidential muddiness to presidential sharpness.

A change in messenger might help convince people that, say, the president’s handling of the Ukraine war has actually been strong, or that the economy is, in fact, humming. It also allows the Democratic ticket to sketch its vision. The pen is in Ms. Harris’s hand.