They are playing the typical "party first, country last" games the GOP always plays.
But the border issues didn't start in 2024. This is the fourth year of Biden's term and a lot of Democrats are criticizing him on this topic.
It's obviously fair to point to the GOP on this, at least partially. But that's not going to win votes for the Dems in November. Actually fixing the border is.
Or, another position is to say "there's actually nothing wrong with the border" (I don't agree with that, but it's a valid stance nonetheless).