The 2020 presidential race is the Democrats’ to lose. If Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE and Alexandria Ocasio-Cortez Alexandria Ocasio-CortezWells Fargo CEO issues apology after saying there was a 'limited pool of Black talent' Brand responds to Trump claim protesters throw tuna cans at police: 'Eat em, don't throw em' CNN's Don Lemon: 'Blow up the entire system' remark taken out of context MORE set the agenda, the Democrats may do just that — lose.

A reelection is about the incumbent, and Donald Trump is the most unpopular incumbent president in modern history. With the election just a year and a half away, that won't change, whatever the shape of the economy or his legal and ethical transgressions.

Unlike most other politicians, President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE doesn't try to expand his base, about 39 percent of voters. While losing the popular vote last time, he won the Electoral College by carrying what Congresswoman Cheri Bustos Cheryl (Cheri) Lea BustosThe Hill's Campaign Report: Biden asks if public can trust vaccine from Trump ahead of Election Day | Oklahoma health officials raised red flags before Trump rally DCCC dropping million on voter education program Clark rolls out endorsements in assistant Speaker race MORE (D-Ill.) calls the "Trump Triers" — voters turned off by Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE and willing to gamble.

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Trump has done little to reassure these “triers.” To win, he needs a third-party candidacy and, especially, a Democratic opponent who misinterprets a lurch to the left among voters and proposes to replace Obamacare with a government-run health care system, a Green New Deal that's neither affordable nor attainable, and empty promises like reparations for the sins of slavery.

That view is undercut by surveys, like that reported by the New York Times Upshot, that rank-and-file party voters are more moderate than liberal social-media activists, or Ann Selzer's Iowa poll showing caucus-goers there are more interested in a candidate who can win than in ideological purity.

Most instructive, last year there were well more than a dozen Democratic House primaries pitting a mainstream progressive against a Sanders left-winger. All over the country — in Maine, Michigan, Virginia, Texas, Iowa, Kansas — the moderates prevailed.

These candidates didn't run corporate-championing, right-of-center planks that Washington lobbyists and Trump-weary Republicans are commending to Democratic candidates. At the top of most agendas was defending and expanding Obamcare.

Republicans are clueless on any health care plan that wouldn't throw millions off coverage and threaten those with pre-existing conditions. Their only lifeline is if a Democratic candidate runs on a single-payer plan, eliminating most private insurance and, according to the Urban Institute, costing $30 trillion over a decade. Whatever the merits — and liberal heath care experts like Ezekiel Emanuel, an architect of the Affordable Health Care Act, are deeply skeptical — it won't fly politically with many of those suburban voters who elected Democrats last November.

There is a liberal and politically appealing alternative: Increase subsidies for lower-income folks; push a public option for those under 65, pressuring insurance companies to offer better coverage; advocate tough cost controls, especially on soaring drug prices, beyond just Medicare negotiating prices; tell insurance companies that if they want to benefit from the profitable Medicare Advantage, they must participate in the health care exchanges.

On taxes, the 2017 Republican tax cut has been a political bust. But proposals to severely jack up the corporate and top individual rates, rather than focusing on broadening the base, are dicey; Sanders wants to raise the top personal rate to 54 percent from 37 percent, and others want to go to 70 percent.

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Again, there's a more palatable and popular approach: Lift the top individual rate to about 42 percent; treat capital gains and dividends like earned income; raise estate taxes back to the lower exemptions and higher rates of ten years ago; close a number of the more expensive loopholes, like the real estate rip-offs, created or continued in the 2017 act.

That could raise more than $1.5 trillion over a decade for real middle-class tax relief, to expand the child tax credit, to help the working poor, and to fund some domestic initiatives — and a bit to temper soaring budget deficits.

Climate change threatens a nightmare for our children and grandchildren. But Rep. Ocasio-Cortez’s Green New Deal says it's an existential threat — it is — and then throws in unrelated measures like a guaranteed job and paid vacations.

Democrats should look to the counsel of former Obama Energy Secretary Ernest Moniz, who says the Green New Deal, carbon-free in ten years, is highly unrealistic while a 25-year rigorous carbon-free plan is ambitious but attainable.

On foreign policy there's an easy solution: Let's care more about allies and alliances than dictators and thugs. Trade will be more vexing; it may be that the Democrats’ only case is that their crazy ideas are not as crazy as Trump's. On immigration — while vowing never to separate children from parents, as Trump did — talk about reviving the 2014 bipartisan Senate comprehensive bill.

If you've covered political campaigns, it's easy to envision the strategy sessions of, say, Sen. Kamala Harris Kamala HarrisHarris faces pivotal moment with Supreme Court battle Nearly 40 Democratic senators call for climate change questions in debates Joe Biden has long forgotten North Carolina: Today's visit is too late MORE (D-Calif.): All the energy is with the left and to win we have to peel off some of the 30 percent Sanders support.

But Trump is the real energizer for Democrats, more than ideology, and no one will get to Bernie's left. If a viable progressive alternative emerges, some of those Bernie "triers" will peel off — and that candidate will be well-positioned to end the Trump era.

Al Hunt is the former executive editor of Bloomberg News. He previously served as reporter, bureau chief and Washington editor for the Wall Street Journal. For almost a quarter century he wrote a column on politics for The Wall Street Journal, then the International New York Times and Bloomberg View. Follow him on Twitter @alhuntdc.