The path to an eventual progressive victory is to take over the Democratic Party, not break it.

Monday night at the Democratic Convention, Bernie Sanders came through for Hillary Clinton in a big way.

His speech contrasted sharply with much of what we heard at the Republican Convention from the candidates Donald Trump defeated, or with the unenthusiastic support for Trump from Republican office-holders like South Carolina Governor Nikki Haley.

Bernie didn’t have to put his heart into it like that. He could have stayed home and watched the convention on TV, like John McCain and John Kasich. He could have made the minimum necessary party-unity statement, like Marco Rubio did by video. Or he could have left his party’s nominee out of the picture entirely, restated his own principles, and then urged his followers to “vote your conscience”, as Ted Cruz did. He could even have denounced Clinton by name, as Jeb Bush and Mitt Romney have denounced Trump.

Green Party candidate Jill Stein has been begging for Sanders to join her, and vigorously campaigning for the votes of his frustrated supporters. So even while keeping his word by tepidly supporting Clinton, he could have winked and nodded at Stein, giving his tacit blessing to Berners who decided to turn Green.

He did none of that. Instead he endorsed Clinton with enthusiasm in prime time.

This election is about which candidate understands the real problems facing this country and has offered real solutions – not just bombast, fear-mongering, name-calling and divisiveness. We need leadership in this country which will improve the lives of working families, the children, the elderly, the sick and the poor. We need leadership which brings our people together and makes us stronger – not leadership which insults Latinos, Muslims, women, African-Americans and veterans – and divides us up. By these measures, any objective observer will conclude that – based on her ideas and her leadership – Hillary Clinton must become the next president of the United States. The choice is not even close.

He reviewed in detail all the issues where a Clinton presidency would be far more progressive than a Trump presidency: the minimum wage, infrastructure, the Supreme Court, the cost of college and student debt, climate change, health care, and immigration reform. And just in case you thought he was making a lesser-of-two-evils argument, he closed with a clear positive statement:

Hillary Clinton will make an outstanding president and I am proud to stand with her here tonight.

He didn’t have to go that far. So why did he? If you find that decision mysterious, or think it requires some dark conspiracy-theory explanation, I have three responses:

Bernie was never as anti-Hillary as you might think.

Hillary has always been more progressive than you might think.

Long-term, Bernie wants to capture the Democratic Party, not break it.

Bernie was never as anti-Hillary as you might think. In the beginning of his campaign, Sanders was relentlessly positive, and refused to go negative on Clinton at all. Recall his line from their first debate:

Let me say — let me say something that may not be great politics. But I think the secretary is right, and that is that the American people are sick and tired of hearing about your damn e-mails.

In the MSNBC debate in March, he prefaced his response to her first comments with:

I have known Secretary Clinton for 25 years and respect her very much.

As the primary campaign got more contentious, there were three levels of criticism of Clinton: fairly mild criticism from Sanders himself, more aggressive statements from his campaign manager Jeff Weaver, and all-out Hillary-is-evil diatribes from Sanders supporters on social media. If you have feel-the-Bern friends on Facebook or Twitter, you know that everything Hillary did seemed sinister to them. Even if she put Elizabeth Warren on the ticket, it would only be to get Warren’s independent voice out of the Senate.

Memory has a way of mixing those criticisms together, so it may seem as if Sanders must be a complete hypocrite to support Clinton now. But Sanders was never running a stop-Clinton campaign. At the beginning, I doubt he thought he had any chance to deny her the nomination.

But he didn’t want a repeat of what happened in 2008, when none of the three candidates who emerged as serious contenders — Obama, Clinton, and John Edwards — proposed single-payer healthcare. As a result, when the ObamaCare discussion began in 2009, single-payer never got a hearing. It was a fringe idea that no “serious” person supported.

This year, if Clinton ran to keep Social Security as it is and the Republicans ran on cutting it, the logical eventual outcome would be to cut it a little less than the Republicans wanted. The idea that it ought to be expanded would be a fringe notion unworthy of discussion. And so on across the board.

Hillary has always been more progressive than you might think. A staple of the Bernie-or-Bust social-media posters is that Clinton is the enemy of progressive change: Whatever they want, she is opposed to, and every move she makes is part of a sinister plan to thwart their ambitions.

But again, if we return to the first debate, Clinton says this to Sanders about healthcare: “We agree on the goals, we just disagree on the means.”

That isn’t just rhetoric. All along, on a wide variety of issues, the debate between Sanders and Clinton has been more about how change happens than about where they want to go. Sanders believes you state your big idea and keep converting people to it until you have a majority, while Clinton believes change happens incrementally: You grab the small amount of progress you can get right now, and hope that its success sets the stage for the next small step. Sanders believes that you call out your opposition and take them on directly, while Clinton looks for proposals that will split the opposition.

If they were football coaches, Sanders’ team would throw deep and often, while Clinton’s team would have a bruising ground game that pushed the ball down the field 3-5 yards at a time. Sanders is always looking to the end zone, while Clinton is looking for the soft spot in the opponent’s line.

So on health care, Sanders has supported a Scandinavian-style single-payer system for as long as he’s been in politics, while Clinton’s 1993 plan was a more complicated public/private mix that she thought she could pass. When it failed, she looked for the opposition’s soft spot and found it: children. The Children’s Health Insurance Program got through Congress in 1997, moving the ball a little further towards universal coverage. And if you were surprised to hear her support putting a public option back into ObamaCare — it was taken out during the congressional debates in 2009 — you shouldn’t be: Her 2008 plan had a public option.

One reason Clinton hasn’t gotten credit for the progressive positions she’s been running on is that across the board Sanders has proposed something bigger and better. His $15 minimum wage trumped her $12 minimum wage — which in a different campaign would have been a bold increase over the current $7.25. Her quarter-trillion-dollar plan to create jobs by building infrastructure looks small next to Bernie’s trillion-dollar plan.

The units of change she calls for have always been smaller than Bernie’s units, but on the vast majority of issues the direction of change is the same.

Long-term, Bernie wants to capture the Democratic Party, not break it. At 74, Bernie is probably too old to run for president again himself. But he sees himself as part of a larger movement that will go on after he bows out of presidential politics. His hopes are not just that the movement will be a way for democracy-loving progressives to express their fine sentiments — the Greens have that covered already — but that it will someday take over the government and implement its policies.

If that’s the goal, the movement has two possible strategies: Take over one of the major parties, or break one (or both) of them and form something new out of the resulting chaos. Both strategies have worked in American history, but the last time the second strategy worked was in the 1850s, when the Whig Party ruptured on the slavery issue, and abolitionists and other slavery-restricting forces created the Republican Party. Abraham Lincoln was an anti-slavery Whig who became a Republican. He was elected president in 1860 in a bizarre four-candidate race that he won with 40% of the vote. If the Southern Democrats hadn’t walked out of the convention that was set to nominate Stephen Douglas, Republican success could have been delayed a lot longer.

The last 150 years have seen third-party challenges by candidates like Eugene Debs, Strom Thurmond, George Wallace, and Ross Perot, but none of them came close to winning the presidency. You can argue that they had their effect by changing the two major parties: Debs’ socialist campaign can be seen as a forerunner of the New Deal, while Thurmond and Wallace were part of the decades-long shift of white Southerners from the Democratic to the Republican Party. But none of them created a new party that outlived their candidacies and replaced either the Republicans or the Democrats.

However, the rise of the primary system in the 1970s created a new possibility: If you can win primaries, you can take over a major party from the inside. Ronald Reagan was the first person to pull that off. At the time, many conservatives thought the Nixon/Ford Republican Party was a lost cause and urged Reagan to lead a Conservative Party. But Reagan ran as a Republican in 1976, narrowly lost the nomination, again resisted the temptation of a third party, and came back to win the Republican nomination and the presidency in 1980. The Republican Party has been the Reagan Party ever since, with the moderate-to-liberal Republicans of the mid-70s going extinct.

In recent years, the Tea Party has been a second wave of conservative revolution within the Republican Party. Despite calling itself a party, it has all along been a faction within the GOP, and has picked up a number of seats in both houses of Congress. Through primaries, it has deposed even members of the Republican congressional leadership like Eric Cantor, and has struck fear into the hearts of non-Tea-Party leaders like John Boehner and Paul Ryan.

Bernie clearly has decided — I believe correctly — that under the current rules the Reagan model is a more viable path to reform than the Lincoln model. The Lincoln Whigs had to spend 1852 and 1856 in the wilderness, and watch a Supreme Court dominated by slavery-supporting appointees produce the Dred Scott decision. By contrast, Tea Partiers have been able to maintain and make use of Republican control of Congress, while building their own revolutionary caucus inside that majority.

A Sanders/Stein Party might or might not outpoll the Democrats in some far-future election. But in the meantime the split center/left vote would virtually guarantee right-wing dominance of the government, and a far-right Supreme Court that would stymie any progressive who might eventually manage to win the presidency.

But the prospect of winning primaries at all levels — producing a strong Progressive Caucus within a Democratic Party that could reasonably aspire to a majority in Congress, and capturing the Democratic presidential nomination for a strong progressive in 2020 or 2024 — seems like a far more promising and less risky path to victory.

That vision explains not just Bernie’s endorsement of Hillary, but also its fervor and his plea for his supporters not to disrupt the Convention with protests: He foresees the day when some future Bernie will be the Democratic nominee seeking party unity. The enemies that he avoids making today may be the friends that candidate will need, if that transformed Democratic Party is going to succeed in winning elections and governing the country.