From today through the California Democratic primary, Sen. Bernie Sanders Bernie SandersKenosha will be a good bellwether in 2020 Biden's fiscal program: What is the likely market impact? McConnell accuses Democrats of sowing division by 'downplaying progress' on election security MORE (Vt.) should run against Donald Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE and the Trump Republicans.

Sanders should treat the remaining presidential primaries as though they are a primary of Sanders versus Trump for the mantle of true populist leader. He should turn the California primary into a general election-style referendum about the future of America, pitting the uplifting and progressive vision of Sanders against the divisive and reactionary Trump nightmare.

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Sanders should lay down the law to the entire Republican establishment and Republican Party. Either they oppose the destructive politics of Trump and make it clear they will vote against Trump in the general election, or they should hereby be dubbed the "Trump Republicans."

Senate Republican Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE (Ky.), and any Senate Republicans who follow his lead and support Trump, are in the leadership class of the Trump Republicans. Republican National Committee Chairman Reince Preibus, who seeks to unite his party behind Trump, is a leader of the Trump Republicans. House Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (Wis.), if he supports Trump after their current distancing from each other, will join the ranks of Trump Republicans.

There is now a clear and linear path for Sanders to play a national and international role, on both the domestic and world stages, as a historically important leader of the progressive movement. Similarly, there is a clear and linear path for the supporters and small donors who back Sanders to play a cutting-edge role in changing the course of American history and leaving a mark — which will continue long after the 2016 campaign is over — on the history of the progressive movement.

Sanders could travel across the nation, from the East Coast to the West Coast and everywhere in between, launching a full-scale campaign for the progressive movement, the progressive agenda and other progressive candidates. Sanders can launch a full-scale assault against Trump and the Trump Republicans and everything they represent about the dark side of American politics.

Trump is saying that many Sanders supporters will back him in November. That is about as likely as the College of Cardinals summoning me to Rome as a future successor to Pope Francis. And speaking of Francis, it was Sanders — not Trump — who was invited to address a Vatican conference about social justice and given the opportunity to briefly chat with the pope about their shared commitment to social justice and economic equality.

Once the presidential campaign is over, my hope is that Sanders could have a far-reaching audience with Francis to discuss at length the possibility of creating a full-fledged international movement on behalf of the values and visions they share.

Sanders is already trouncing Trump in the battle of ideas, which is why he leads Trump by gigantic landslide margins in match-up polling. He should directly and aggressively challenge Trump in future primaries with independent voters and he should call on Republican voters in upcoming primaries to vote for him rather than Trump, where possible, to register their protest against Trump.

In California, Sanders should urge Republicans to take advantage of their opportunity to change their registration during the coming weeks and register as non-party voters to "feel the Bern" and reject Trump on primary day, sending a message to Republicans in Washington that Trump guarantees the road to division and disaster for America and a landslide defeat for the GOP.

Instead of criticizing likely Democratic nominee Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE, Sanders should concentrate all of his fire on exposing the phony populism of Donald Trump, calling for the defeat of Trump Republicans at all levels of politics, and carrying the banner of progressivism in support of progressive candidates throughout America.

Budowsky was an aide to former Sen. Lloyd Bentsen (D-Texas) and former Chief Deputy Majority Whip Bill Alexander (D-Ark.). He holds an LL.M. degree in international financial law from the London School of Economics. Contact him at brentbbi@webtv.net.