In May 2015, when Donald Trump was polling at 5 percent in the Republican presidential primary, he told a reporter in Des Moines, Iowa, “I’m not going to cut Social Security like every other Republican, and I’m not going to cut Medicare or Medicaid.”

It’s easy to forget, but promising to leave benefits for seniors alone was part of Trump’s campaign message from the beginning. Things have changed. At the annual ruling-class summit in Davos, Switzerland, last week, a reporter asked Trump if “entitlement cuts” would “ever be on your plate.” Trump answered that “at some point they will be,” adding, “At the right time, we will take a look at that.”

Some of the mainstream press is treating these remarks like a brand new development. That’s not quite accurate. As Eric Levitz points out in New York magazine, Trump’s about-face on entitlements occurred very early in his presidency. His administration has made several attempts in the last three years to cut spending on Social Security, Medicare, and Medicaid, in direct violation of his campaign promises.

The newsworthy turn of events here is that Trump, who has previously expressed concern that voters will catch onto his administration’s aggressive austerity agenda, seems to have slipped up and admitted it.

Compared to European social democracies, the United States has an underdeveloped (and underappreciated) welfare state. In part, this is because so many of our programs are obscure, complicated, and narrow — hard to see, hard to use, hard to defend. But guaranteed benefits for the elderly are exceptions to this rule, eliciting strong popular support.

This, of course, refers to Social Security and Medicare, the most universal and most popular social programs in the country. But it also extends to Medicaid, because despite some of its design flaws, Medicaid is a huge program that covers massive numbers of people, including millions of seniors who rely on both Medicare and Medicaid.

Because large numbers of Americans need, like, and care about these programs, Trump’s betrayal of them is an electoral weak spot — one that his opponent should ruthlessly exploit in the upcoming general election. But not all contenders will be equally capable of credibly attacking Trump on entitlements. If we want to hit Trump where it hurts, Bernie Sanders is the candidate to deliver the blow.

Of all the candidates, Bernie has the longest and strongest record of defending and fighting to expand vital public programs for seniors. Throughout his congressional career, he has voted against every effort, no matter how sneaky or nearly imperceptible, to cut or privatize Social Security and Medicare.

And he has long insisted that not only must these programs be protected, they should be expanded.

Famously, he has popularized the demand to improve Medicare and expand it to every American — the exact opposite of Trump’s under-the-radar austerity agenda. Similarly, he founded the Defend Social Security Caucus, co-founded the Expand Social Security Caucus, and has introduced legislation to improve and strengthen Social Security.

In 2006, as President George W. Bush attempted to privatize social security, Sanders spoke out, saying, “Social Security is the most successful anti-poverty program in history. We must strengthen it, not destroy it.” He said much the same thing in 2010, when it was not President Bush attempting to implement cuts to Social Security but a bipartisan deficit-reduction commission appointed by President Barack Obama.

Sanders stood on his feet for eight hours and filibustered against the legislation that resulted from the bipartisan negotiations. He repeatedly warned of its implications for Social Security, saying:

Social Security has been an enormous success. It has done exactly what those people who created it have wanted it to do — nothing more, nothing less. It has succeeded. It has taken millions of seniors out of poverty and given them an element of security. It has also helped people with disabilities maintain their dignity. Widows and orphans are also getting help. For 75 years it has worked well.

Sanders added:

The Republicans will tell you: “Oh, we have a great plan to deal with [the deficit]. We are giving tax breaks to millionaires. But now what we are going to have to do is start making deep cuts in Social Security” — and that deficit reduction commission started paving the way for that, very substantial cuts in Social Security — “Maybe we will have to raise the retirement age in Social Security to 69 or 70. Maybe we will have to make cuts in Medicare. Maybe we will have to make cuts in Medicaid.” . . . I certainly will do everything I can to prevent that.

Elsewhere in the speech, Sanders criticized not only the president but also the vice president for compromising on Social Security and Medicare to appease Republicans. The vice president, of course, was Joe Biden — and it was Biden who had been especially eager to put Social Security and Medicare on the table in negotiations with Republicans.

In the past few weeks, Biden has forcefully denied ever trying to cut Social Security. This is dishonest. In contrast to Sanders, Biden has attempted to cut Social Security, Medicare, and Medicaid many times throughout his career. He tried it the 1980s, 1990s, 2000s, and 2010s. Take it from Biden himself:

When I argued that we should freeze federal spending, I meant Social Security as well. I meant Medicare and Medicaid. I meant veterans benefits. I meant every single solitary thing in the Government. And I not only tried it once, I tried it twice, I tried it a third time, and I tried it a fourth time. Somebody has to tell me in here how we are going to do this hard work without dealing with any of those sacred cows.

Right now, Sanders and Biden are each other’s main competition for the party’s nomination. But if Biden wins, Trump will have an opponent who is guilty of putting entitlements on the chopping block, just as he is. Given how popular these programs are, nominating Biden would be a waste of potential ammunition against Trump. Nominating any of the other candidates, too, would be a lost opportunity, since none of them have the decades of experience fighting to defend these popular social programs that Sanders has.

No matter their political ideology or party affiliation, hundreds of millions of people rely on Social Security, Medicare, and Medicaid. When Trump ran in 2016, promising not to undermine these programs was a huge selling point. Pointing out in 2020 that he has attempted to undermine them, and that he plans to continue to do so, will be hugely advantageous in the effort to defeat him. Bernie Sanders is far and away the best candidate to deliver this message; failing to nominate him would be a giveaway to Donald Trump.