Things got a little confusing in the debate when former Housing Secretary Julián Castro accused former Vice President Joe Biden of forgetting what he had said earlier on health care — an exchange that drew attention for perhaps implying an attack on Biden’s age and memory.

The clash came after Castro criticized Biden’s health care plan for not automatically enrolling all uninsured Americans in a Medicare-like plan, as Castro says his plan would do.

“The difference between what I support and what you support, Vice President Biden, is that you require them to opt in and I would not require them to opt in, they would automatically be enrolled — they wouldn't have to buy in,” Castro said. “That's a big difference, because Barack Obama's vision was not to leave 10 million people uncovered.”

Democratic presidential candidate former Vice President Joe Biden speaks during the Democratic presidential debate on Sept. 12, 2019 in Houston. Win McNamee / Getty Images

When Biden protested that “they would not have to buy in,” Castro said he was contradicting an earlier claim that people would have to “buy in” to Medicare. Biden responded, “I said if they can’t afford it!”

Two issues are at play here. One is the narrow issue of what Biden said earlier; two is a disagreement between the two on health care policy.

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To parse this requires an understanding about the difference between their plans. Castro, according to the outline published on his website, would enroll newborns and people who lose their insurance automatically in a Medicare-like plan as a default.

Biden’s proposal is a little different. According to his campaign, people who qualify for Medicaid under Affordable Care Act expansion would automatically qualify for a zero-premium Medicare-like plan, as opposed to people at higher incomes who would have to pay at least some premium. And he would automatically enroll “individuals when they interact with certain institutions (such as public schools) or other programs for low-income populations (such as SNAP).”

Before the exchange with Castro, Biden said “anyone who can’t afford it gets automatically enrolled in the Medicare-type option we have,” which is true if you accept his plan’s definition of “can’t afford it.” He also said “you automatically can buy into this” if you lose your job and insurance, which is also true in that someone who lost his or her job would be given the opportunity to buy a Medicare-like plan with government help, although would not be enrolled automatically.

This reference to two situations — one, a person who loses their job, and two, a person who can’t afford insurance — created a mix-up later when they argued over both issues simultaneously.

When Castro referenced 10 million residents who would potentially be without insurance under Biden’s plan, Biden protested “they do not have to buy in.” Castro took his initial answer to mean Biden was backtracking, but Biden immediately and repeatedly clarified he was referring to people at low incomes who would get their plans for free and be automatically enrolled if they made use of anti-poverty programs. Castro kept challenging him on the supposed contradiction anyway, even after he had cleared it up.

Castro was also making a separate point, which he articulated at the end, which is that Biden’s plan would not automatically enroll everyone in a Medicare-like plan who doesn’t have insurance, leaving some people uncovered. This would potentially be by choice, though, not just by oversight: Some Americans would elect not to pay the premium for a Medicare-like plan even if it was capped at 8.5 percent of their income, as Biden's plan would do. Biden's campaign estimates 97 percent of people would be covered.

“It automatically enrolls people regardless of whether they choose to opt in or not," Castro said." If you lose your job, for instance, his health care plan would not automatically enroll you. You would have to opt in."

Here Castro was correct, but they didn’t get to debate it further. People who lost their job would have access to a Medicare-like plan under Biden’s approach, but wouldn’t be automatically enrolled unless they hit those other qualifiers in his proposal. But Biden also described his plan throughout their exchange largely accurately, noting it was free and enrollment was automatic only at lower incomes.

However, the main issue Castro was raising — whether Biden’s plan truly covered everyone or left millions without insurance — was not just about automatic enrollment. A lot of it has to do with Biden’s decision not to subsidize care for undocumented immigrants in his plan, which they didn’t discuss onstage.

The end result was a debate where two candidates with some differences were largely talking past each other. Castro articulated a real divide, but Biden also described his plan largely accurately and did not appear to backtrack on his earlier answers in a significant way.