Ryan J. Rusak

‘Are you forgetting already?’ Castro’s debate jab at Biden’s age was a step too far.

Julián Castro had the potential breakout moment he badly needed in Thursday night’s debate. The question will be: By going there against Joe Biden, did he go too far?

The topic was health care. Biden and Castro, the former San Antonio mayor, were debating the fairly narrow point of whether Americans would be able to “buy in” to Medicare or would be automatically enrolled.

Castro insisted that Biden had described his plan as a buy-in. And then he played the senility card, asking the 76-year-old former vice president: “Are you forgetting already what you said just two minutes ago?”

He said it twice, for good measure. Whether that means it was a planned line or he liked it so much he wanted to drive it home, it was impossible to ignore.

Castro’s comment drew a hushed “ooh” among the reporters covering the debate. And it seemed out of place, as this time, at least, Biden was offering clear, crisp answers and taking the debate directly to his front-running opponents on the issue.

And Castro wasn’t entirely right. Biden did talk about a buy-in, but he also said people could automatically enroll in his expanded Medicare plan.

Still, Biden’s campaign trail misstatements have been a bubbling problem for him. The blunt question behind them: Is Biden, at 76, too old to be elected president?

Castro is the first candidate to directly raise it. And he did so with a sharpness that may turn off some Democrats whose most important qualification in judging a candidate is whether they can beat Donald Trump. It’s Biden’s strongest selling point.

The former vice president has also been running hard on the legacy of being the partner who helped Barack Obama govern. He knows that Obama remains the most popular figure in his party (well, maybe other than the former president’s wife, Michelle).

But Castro aimed to remind Democratic voters that Biden was not the only candidate who served Obama’s administration. Castro was Obama’s housing secretary.

On health care, he told Biden, “I’m fulfilling the legacy of Barack Obama, and you’re not.”

Biden retorted: “That will be a surprise to him.”

Castro is going to get a lot of attention for his jabs. But in going negative, he mangled the facts, and he should expect a backlash.

Note: Updated Friday morning to correct that Biden talked about both a buy-in and automatic enrollment to his Medicare plan.

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Ryan J. Rusak is opinion editor of the Fort Worth Star-Telegram. He grew up in Benbrook and is a TCU graduate. He spent more than 12 years as a political journalist, overseeing coverage of four presidential elections and several sessions of the Texas Legislature. He lives in east Fort Worth.