Nominating Sanders would require either a Romney-esque flip on immigration, or dispiriting the Democratic base on the issue that largely defines and fuels their opposition to Trump.

According to The New York Times, “mainstream Democrats are increasingly worried that their effort to defeat President Trump in 2020 could be complicated by [Bernie] Sanders, in a political scenario all too reminiscent of how Mr. Trump himself seized the Republican nomination in 2016.” Sanders pays lip service to the idea of unity, but has warned supporters he is also fighting establishment Democrats.

Bernie is embroiled in a bitter feud with Clinton loyalists at the Center for American Progress (CAP), which has been criticizing the socialist’s Medicare-for-All proposal behind the scenes. (There is little question where the Times stands in this battle; its hit piece uses CAP President Neera Tanden’s 78-year-old mother to attack her.)

The “Stop Sanders” Democrats will turn out to be as ineffectual as NeverTrump Republicans were in 2016 unless they find a line of attack that is not simply a grievance of the party’s establishment. Sanders supporters are about as likely to ditch Bernie over his millionaire status as Trump supporters were affected by the bankruptcies in his business past. Nor are they likely to care about the details of his single-payer health-care bill. But once Bernie’s opponents understand the roots of his success, they may find a potent issue staring them in the face.

There are two major reasons Sanders is near the Democrats’ center of gravity. First, his socialism (or “social-ism“) largely expresses a vision Democrats have held for at least 50 years and often longer. Second, because his vision is old, it remains rooted in class, rather than the identity politics of the New New Left. For some, this second reason is a feature; for others, it is a bug.

The potential fault line for Sanders among Democrats may be his position on immigration:

Sen. Bernie Sanders campaigns in Oskaloosa, IA: "If you open the borders, there's a lot of poverty in this world, and you're going to have people from all over the world. And I don't think that's something that we can do at this point. Can't do it." pic.twitter.com/INF9GopzIe — The Hill (@thehill) April 7, 2019

Bernie’s stance against open borders is not where many Democrats are now, especially young progressives and democratic socialists like Rep. Alexandria Ocasio-Cortez:

Rep. @AOC: "I think 'Abolish ICE' is a call to action on several levels. One is the literal interpretation of all abolishing ICE, which I support…I don't believe that an agency that systematically & repeatedly violates human rights — I don't think that agency can be reformed." pic.twitter.com/YyOQCSA3lA — The Hill (@thehill) April 16, 2019

Granted, the woke are as over-hyped as the “Stop Sanders” types are likely to be. But the younger, woker set is likely to be a key component of Bernie’s coalition.

Per HarrisX, Generation (aka age) is THE divide in the Dem primary right now. This is an average of the last few days… Bernie Sanders has got the young and Joe Biden has got the old. (Note other polls confirm this.) pic.twitter.com/6cBX3qz1hk — (((Harry Enten))) (@ForecasterEnten) March 12, 2019

Moreover, the open borders position is held more broadly among Democratic leadership. House Speaker Nancy Pelosi has repeatedly called a border wall “immoral.” Senate Minority Leader Chuck Schumer has called the wall “medieval.”

It is obvious to anyone paying attention that Democrats’ newfound extremism against border security is a reaction to President Trump, who made it his signature issue in 2016. More than any other subject (excepting possibly “Russiagate”), Trump’s immigration policies embody the personal qualities Democrats loathe about Trump.

For Democrats, Trump’s determination to secure our border and crack down on illegal immigration represent his racism, nativism, Islamophobia, and general cruelty. His immigration policies outrage the party faithful, and none more than those marinating in left-wing identity politics.

Viewing the 2020 campaign from this perspective, the Democrats nominating Sanders would be not unlike Republicans nominating Mitt Romney in 2012. The GOP suffered steep losses in 2008, but roared back to reclaim Congress in 2010 based on widespread opposition to Obamacare. Having championed a mandate-based health system as governor of Massachusetts, Romney was effectively neutered on this key issue, dampening partisan enthusiasm for his candidacy. Nominating Sanders would require either a Romney-esque flip on immigration, or dispiriting the Democratic base on the issue that largely defines and fuels their opposition to Trump.

Sanders can try to spin his immigration position as a feature rather than a bug. Republicans tend to win on immigration when the question is whether America should have borders and enforce them. Democrats tend to gain when the issue becomes what to do about those who have already crossed into our country illegally (e.g., family separation, a path to citizenship, etc.)

By rejecting open borders, a Sanders-Trump debate would play out on more Democratic turf. Sanders might also argue that his position is a better fit to attract Obama-Trump voters in the Rust Belt and Midwestern states Hillary Clinton lost.

This will be a difficult sell, however, to Democrats who have elevated the notion of open borders to a moral principle. Again, the parallel to the right’s attitudes regarding Obamacare is instructive.

When each party base has lacked the power to enact legislation, it has been easy to embrace maximalist positions. Tea Party Republicans generally sought to repeal Obamacare without consensus about a replacement. Progressives and socialists want to abolish Immigration and Customs Enforcement and tear down the wall we already have.

Only after a party gains effective control of the government do political realities intrude. It is a psychology that does not aid Sanders in winning the Democratic nomination, let alone a general election.

There is no guarantee the neoliberals and woke identitarians can deny Sanders the Democratic nomination by putting him in a vise on immigration. After all, Romney did win the GOP nod in 2012, despite his weakness on Obamacare. But Bernie’s opponents have failed to come up with a better idea so far.