alito is playing in our faces because he knows there’s nothing we can do about it and he has total contempt for the idea that he might be accountable for anything he does
Impeachment starts in the House, so that's right out, at the moment. However, the Senate Judiciary could hold hearings. Use them as a means to move public opinion and raise the salience of this issue.
They've ruled out expanding the court, which is the only realistic way to reduce the conservative power, so the worst they can do are public scoldings.
Ds need 51 non-Manchin, non-Sinema seats in the Senate and a willingness to abolish the filibuster. (Of course, that's ignoring the other probably at-least-half-dozen Senate Ds that are waiting in the wings to assume Manchin's and Sinema's mantle)
And the other stuff, too.