In Wednesday night’s Democratic presidential debate, the subject of Barack Obama came up in a way that made lots of people uneasy. It began when Joe Biden was asked a question about the high rate of deportations during the Obama presidency, which Bill de Blasio, Julián Castro and Cory Booker then used to criticize Biden.

As Booker put it, “Mr. Vice President, you can’t have it both ways. You invoke President Obama more than anybody in this campaign. You can’t do it when it’s convenient and then dodge it when it’s not.”

If you were following social media at that moment, you would have seen a lot of liberals express their dismay, not so much at the substance of the criticism of Obama’s immigration record but at the very idea of criticizing Obama in a Democratic primary. It was, many believed, a strategic mistake. Particularly considering that Obama remains the most beloved Democrat in America (unless you count his wife, Michelle).

So is it acceptable for a Democrat to criticize Obama? And should it be?

Just to lay my own cards on the table, I think Obama had some important shortcomings but was overall an excellent president. I’d even go so far as to say he was the best president of my lifetime, since I’m a liberal and that means I rate him ahead of Bill Clinton and Jimmy Carter.

In addition to having a long list of accomplishments, Obama embodied nearly every character trait you’d want in a president. He was smart, thoughtful, compassionate and concerned more with the long term than the day’s news. His personal integrity was unimpeachable, and he conducted himself with grace and class every day he served, no matter how despicable the attacks he endured.

And of course, Obama looks even better by comparison with our current president, not only the most corrupt person to ever sit in the Oval Office but a walking collection of character flaws who is possessed of not a single identifiable human virtue.

But that doesn’t mean Obama was perfect, since no president was or ever will be. And if Democrats want to have a serious discussion about what they want to do with the presidency the next time they have it, they not only can discuss the shortcomings of Obama’s tenure, they have to.

Sen. Kamala Harris has failed to recognize her problematic decisions as a former prosecutor, making her Joe Biden attacks hypocritical, argues Joy Sharon Yi. (The Washington Post)

To take one example, any list of Obama’s mistakes has to include his failure to move aggressively on filling judicial nominations. While later in his tenure Republicans made it all but impossible for him to do so, culminating in the unconscionable refusal to allow Supreme Court nominee Merrick Garland to even get a hearing, in Obama’s first term it simply wasn’t a high priority for the administration. As this 2012 article described it, “Mr. Obama moved more slowly and sought relatively moderate jurists who he hoped would not provoke culture wars that distracted attention from his ambitious legislative agenda.”

Then when Republicans cranked their obstruction up to 11, Obama was left with large numbers of vacancies he couldn’t fill. The result was that when Donald Trump took office, he was able to quickly pack the courts with young extremist conservatives who will be on the bench for decades.

If you’re a Democratic voter, you should want to hear from your candidates about this history and what they intend to do about it. Do they appreciate the magnitude of the problem, both the importance of the courts and the necessity of having a strategy to deal with Republican obstructionism that doesn’t rely on hope? Are they going to make the judiciary as much of a priority as Trump has?

You could say the same about some of the other areas in which Obama fell short, from cracking down on Wall Street to mishandling the rollout of the Affordable Care Act. Talking about those things doesn’t diminish the credit he deserves for all the good things he did; it shows that a candidate is trying to learn from the past and thinking seriously about the challenges of governing.

Of course, you can do it in a shallow way, if you’re just looking for a bludgeon to hit Biden with. But Booker was right: If Biden is going to make the fact that he served as Obama’s vice president the centerpiece of his appeal to Democratic voters (which he is), then he has to show that he understands what went wrong as as well as what went right during those years.

The man who once mocked Rudolph W. Giuliani’s abysmal 2008 presidential campaign by saying “There’s only three things he mentions in a sentence: a noun and a verb and 9/11,” could be in danger of receiving the same criticism, with “Barack Obama” substituted for “9/11.”

But this is something every candidate should be grappling with. Democratic voters need to know more than how much they loathe Trump (which they should) or how much they admire Obama (which they also should). Planning and executing a successful presidency make up the most intricate and demanding task any one of them will ever face. We should know what goes into their thinking, whether they understand the history of those who have done it before, and how they intend to go about it. If they can’t tell us that, they don’t deserve anyone’s vote.

Read more: