(Daniel Acker/Bloomberg)
Opinion writer

Hillary Clinton won a decisive string of victories yesterday in Florida, Ohio, North Carolina and Illinois, and she remains slightly ahead in Missouri, pending a possible recount. Clinton expanded her lead in pledged delegates to around 700, which means Bernie Sanders would have to win at least three fourths of the remaining delegates to gain a majority — potentially putting the nomination out of reach for him.

The Vermont Senator has vowed to press on, arguing that he’s favored to win in a string of upcoming states and that he’ll be able to use the resulting momentum to persuade super-delegates to flip to his side at the convention.

In an interview with me today, Clinton’s chief strategist, Joel Benenson, dismissed those arguments. He insisted that Sanders has no viable path left to the nomination, leaving him with tough choices about whether he should continue, what he hopes to accomplish, and whether he should keep attacking Clinton as hard as he has been so far, given that he can’t win. Benenson also argued that the results so far counter the conventional wisdom that Sanders’s economic message is stronger than hers.

Benenson also shed new light on how the Clinton team views the looming battle with Donald Trump, insisting that analysts are wrong in arguing that she might be vulnerable to Trump making inroads among blue collar whites in the industrial Midwest, and maintaining that if anything, Trump might enable Clinton to pick off a few states that have been solidly in the GOP camp. A transcript of our conversation, edited and condensed for length and clarity, is below.

THE PLUM LINE: What’s your read on the meaning of last night and where this goes from here?

JOEL BENENSON: After last night, Hillary Clinton has a delegate lead that puts the race effectively out of reach for Senator Sanders. We now have a more than 300 lead among pledged delegates. Even if he won California, New York, and Pennsylvania by 20 points, that would still leave him more than 120 pledged delegates behind Hillary Clinton.

Senator Sanders has voiced his intention initially to stay in the race. There are states that he may do well in. But he and his team will have to make a decision about what they’re trying to accomplish. From a message perspective, Hillary Clinton overcame what was increasingly a negative and distortive attack from Senator Sanders.

PLUM LINE: Are you suggesting that he is going to rack up some victories in the future?

BENENSON: There are some states where we expect him to do well. But the reality is that we have outperformed him in almost every large state. You have to win delegates. Even if he wins some states, and he wins them close, you don’t pick up any delegates anymore. If Sanders win caucuses in some states, they just don’t have enough delegates to close the gap of 300 pledged delegates.

PLUM LINE: In some of the earlier contests, he outperformed Senator Clinton substantially among young voters. In the general election, doesn’t that raise the possibility that she is going to struggle to motivate those people?

BENENSON: She’s going to work very hard to keep those people motivated. If they care about the issues Senator Sanders cares about, the only choice for the future of the country would be to support Hillary Clinton against any one of the Republicans. There is no question he has dominated with 18 to 29-year-old voters. But we have repeatedly won with voters over the age of 30.

Are 18 to 29-year-old voters an important part of the Democratic coalition? Of course they are. And we’ll work very hard to get them to turn out. But it is false to translate primary results into general elections. We absolutely are going to work out tails off to keep Senator Sanders’s voters engaged and excited.

PLUM LINE: You mentioned that the math isn’t there for Senator Sanders. Are you suggesting that Sanders should leave the race now or tone down the criticism of Clinton?

BENENSON: Any decisions about his campaign are rightfully his. He has worked very hard. His campaign decided to be increasingly negative and increasingly explicit in assailing Clinton. The negative strategy backfired. The question will be, will he return to a tone that is more issue-focused, rather than attack-based?

PLUM LINE: But aren’t some of his attacks expressions of legitimate policy differences?

BENENSON: We’ll have policy differences with him, and he’ll have policy differences with us. But when you start going down a personal character dimension, which is what they did in some places, that’s a path that I suspect their campaign is rethinking this morning.

PLUM LINE: Isn’t it fair to say that the arguments between them have exposed some weaknesses in her economic message?

BENENSON: If anything, it showed weaknesses in his. When you talk to people who work in manufacturing states, they know that we need to sell around the world. Hillary Clinton’s message in some of these Midwestern states, which made a real difference, is that America has what it takes to compete in the global economy, if we make the right investments, reinvigorate manufacturing, and negotiate and enforce tough trade agreements.

I don’t think it helps Senator Sanders in Ohio that he calls the Export-Import Bank a boondoggle. People who work on assembly lines understand that they need their jobs protected, but they also need for the goods they make to be sold overseas.

PLUM LINE: How do you square that argument about the need to compete globally with her expressed skepticism of the Trans-Pacific Partnership?

BENENSON: What she does is actually read the agreements when they’re finished, to see whether they are strong enough in protecting American jobs and workers and making wages rise here. If they meet those standards, she supports them. If they don’t, she doesn’t.

PLUM LINE: The general election — do you guys expect it to be Trump, or are you envisioning other scenarios as well?

BENENSON: Donald Trump is a very unconventional candidate, to be sure. But when you come down to the big issues that we’re debating, every one of these Republicans is aligned with the most extreme policies of the Republican Party economically. They all want to give hundreds of billions, if not trillions, in tax cuts to those at the top. They have opposed everything that helps working people get ahead — raising the minimum wage, equal pay for women. They have offered no plans to reduce the crushing burden of debt for people going to college.

They are on the wrong side of the majority of Americans on opposing comprehensive immigration reform, opposing marriage and anti-discrimination laws for LGBT Americans, and in continuing to deny climate change. They have their heads in the sand on social issues. Those are fights that we would welcome against any of these candidates.

PLUM LINE: Isn’t it fair to say that Trump is almost leading a movement here, and that he could have some appeal to working class whites in some states in the industrial Midwest?

BENENSON: He puts more red-to-purple states in play for us. There are states that Democrats have been within striking distance of in presidential elections. We won North Carolina one of the last six times. That’s a state that Trump will have a hard time holding. Obama lost Georgia by seven points in 2008. With its changing demographics — its young people and increasing minority population — that state becomes very problematic for them.

I don’t think there’s a single battleground state that he makes more competitive. Those states hinge on swing voters who are economically more aligned with where the Democratic Party is economically and socially.

PLUM LINE: Give us the bottom line on the blue-collar-white question. In places like Pennsylvania, Ohio, and Wisconsin, could Trump run up a larger margin among working class whites than Romney did against Obama in 2012, and does that matter?

BENENSON: I don’t believe so. Donald Trump and Ted Cruz have a high number of people in their own party who would not be satisfied with them as the nominee. For moderate Republicans, there does not appear to be a place in their party anymore. They do not have a candidate at the top of their field right now who is appealing to moderates in their party. Those are blue collar whites.

They are not monolithic. Blue collar, working class Americans happen to be Democrats, Republicans and independents. We actually have messages and candidates that appeal to those voters more. They are not trickle down, radical economic voters. They are more middle of the road, mainstream voters.