The point is, and I think Yglesias is correct about this, abortion isn’t as potent an issue now as the pandemic was back then. It may still be significant in certain races but it’s not going to unify the party the way the absurd fantasy that Joe Biden would magically “shut down the virus” did four years ago.
Meanwhile, unless something actually changes, you’re going to keep getting bad news about the border crisis every month between now and the election. Maybe sanctuary city mayors will be able to discipline themselves to not complain about it as loudly as they have been lately (or maybe not). But there’s a real chance the border will still be on people’s radar in November. In short, Democrats are probably right to worry.