Bernie Sanders has plenty of sound reasons for continuing his presidential campaign, but now that Donald Trump is the apparent Republican nominee, he needs to make a change in tone.

Sanders still has a chance — albeit a vanishingly small chance — of winning more pledged delegates to the Democratic convention than Hillary Clinton. And polls show that Sanders’ supporters want him to stay in the race, by a huge margin. “Bernie thinks he has a responsibility to the millions of people who have turned out for him,” his top strategist, Tad Devine, told me last week.

But the Sanders campaign was never solely about winning the Democratic nomination. The Vermont socialist’s other goal was to build a progressive grass-roots movement and to push the Democratic Party to the left.

On that count, Sanders has mostly succeeded. His campaign has reawakened the progressive wing of the Democratic Party and forced Clinton to move leftward on economic issues including Social Security and trade.


Now he wants to continue that process by amassing yet more delegates, even if they turn out to be a minority at the convention.

“If we don’t win, we intend to win every delegate we can so that when we go to Philadelphia, we will have the votes to put together the strongest progressive agenda that any party has ever seen,” Sanders said last month.

He wants the Democratic platform to include a call for a $15 federal minimum wage (which Clinton does not support) and a commitment to sweeping campaign finance reform.

His motivation isn’t only ideological; Sanders argues that the party needs to tack to the left if it is to mobilize the voters — especially young voters — it needs to win in November.


So even if he can’t win the nomination, Sanders’ other goals require him to keep campaigning as long as possible.

The problem isn’t Sanders’ persistence; it’s the harshness of his attacks on Clinton.

His victory speech after the Indiana primary last week

included a seven-minute attack on Goldman Sachs, the Wall Street firm that famously paid Clinton $225,000 per speech.

“It must be a speech written in Shakespearean prose,” Sanders said, scoffing.


Clinton’s fundraising practices and speech fees are legitimate issues, but Sanders has come perilously close to accusing Clinton of corruption — an argument that will make it harder for his supporters to vote for her in November.

Devine told me the senator is still angry about some of the attacks he took from the Clinton campaign, particularly the charge that he owes an apology to victims of gun violence for his record on gun control.

The problem isn’t Sanders’s persistence; it’s the harshness of his message.

“We’re not the ones who started this back-and-forth,” Devine said. “Bernie got pushed to a place where he wasn’t originally going to go.”


But unless Sanders wants to sabotage the Democratic Party — and I don’t think he does — he needs to dial back a notch.

Sanders faces other difficult decisions on the road to the July convention in Philadelphia.

One is whether to continue his campaign after California votes June 7. If he pulls off a string of upset victories in the remaining primaries and finishes ahead in the race for pledged delegates, he’ll try to persuade superdelegates to support him — and that’s reasonable.

Sanders’ aides, however, say he might pursue a superdelegate strategy even if he finishes behind — a recipe for a divisive battle. (It would also make Sanders, who long argued that pledged delegates should determine the outcome, look hypocritical.)


The candidate’s forces are already asking the Democratic National Committee for changes in the convention’s standing committees, which set the convention rules and draft the platform. They complain, with some justice, that the members of those committees have been stacked in Clinton’s favor. And they’ve warned that a convention that looks unfair will send the wrong message to Sanders’ supporters.

“If you’re going to back us into a corner, we’re not going to be happy,” Devine said. “It’s a two-way street. Is this going to be a period of accord or discord? My preference is to find common ground.”

Sanders says he doesn’t want to be a spoiler if Clinton wins the nomination fair and square.

“Of course the party needs to be unified, and it will be unified after the convention in July,” he said last week.


“Hillary Clinton and I agree … that we will do everything we can to make sure that a Republican does not win the White House. And I will knock my brains out, I will work seven days a week to make sure that does not happen — if I am the nominee, and if I am not the nominee.”

If he means that, this would be a good time to start acting like it — for both Democratic candidates.

doyle.mcmanus@latimes.com Twitter: @DoyleMcManus

Follow the Opinion section on Twitter @latimesopinion and Facebook