Fehrnstrom famously replied:

Well, I think you hit a reset button for the fall campaign. Everything changes. It’s almost like an Etch-A-Sketch. You can kind of shake it up and restart all over again.

In practice, though, with virtually everything a candidate says now recorded for posterity, it has become increasingly difficult to evade past statements.

The possible costs of the Democratic candidates’ commitment to decriminalization of border crossing are evident in a NPR/PBS NewsHour/Marist Poll conducted July 15-17. It found that all voters oppose decriminalization by better than two to one, 66-27.

Along similar lines, the liberal, pro-Democratic Center for American Progress issued a report on Monday warning that progressive supporters of liberalized immigration “have ceded powerful rhetorical ground to immigration restrictionists, who are happy to masquerade as the sole defenders of America as a nation of laws.”

There is, according to the center’s report,

a growing sense among some policymakers, as well as among many in the pro-immigrant advocacy community, that the entire enforcement apparatus must be unwound. Certainly, enforcement reforms are necessary, as the following sections of this report explain. But the move to reject enforcement entirely — even in theory — only fuels louder calls for maximum enforcement.

It is not as if Democrats are lacking powerful immigration issues on which to run. An April University of Maryland “Study of American Attitudes on Immigration and Refugees” found that the Trump administration’s family separation policies are opposed 64-25, including by independent swing voters (67-18) and even by Republicans whose partisan allegiance is not strong (51-34). Only strong Republicans support the policies, 55-26.

Advocacy for this year’s progressive causes by a number of the Democratic presidential candidates has become a source of anxiety for some well-respected, mainstream Democrats.

Paul Begala, a Democratic strategist, argued that two factors — fund-raising demands and the effect of the social media on candidates and their staff — are turning the nomination contest into “some kind of purity game to see who can be the most leftist.”

In the case of social media, Begala declared:

Democratic Twitter is dominated by overeducated, over-caffeinated, over-opinionated pain-in-the-ass white liberals. Every candidate, and every staffer, checks Twitter and other social media scores of times a day.

The second and more significant factor is what Begala described as the unintended consequences of “the obsession with small donors.” Democrats legitimately “want to break the stranglehold of big money,” Begala wrote, but

when the D.N.C. made accumulating small donors a centerpiece to debate eligibility among two dozen potential candidates, that’s when the unintended consequence kicked in. Small donors are often more motivated, more activist, more engaged, more ideological. In short, more leftist. They’re less likely to send in five bucks to a candidate who says, “I’m going to preserve Obamacare, maintain private insurance, and add a public option so anyone who wants to can join Medicare” — even though that’s where most Americans and most Democrats are.

Begala said he has

spoken with numerous state party officials and congressional campaigners who have traced the leftward lurch of the presidential candidates to the small donor problem. The tyranny of the small donor cannot be underestimated.

In a July 17 article in The American Prospect, “Can the Democrats Define Their Own Cause? Or will Trump define it for them?” Paul Starr, a professor of sociology and public affairs at Princeton, warned:

Some of the leading 2020 Democratic presidential candidates didn’t help their cause in the June debates by taking a series of unpopular positions, such as banning private health insurance, providing insurance to the undocumented, and decriminalizing border entry. They’re giving Trump and the Republicans plenty to work with.

In an email, Starr described these developments as “a genuine puzzle.”