> I mean what's the alternative theory to judicial review?

In the actual Constitution? There's no judicial review mentioned. At all.

> other than voting harder?

That's pretty much it, until Marbury v. Madison and the Supremes decided they were it.

There are all kinds of gaping holes in the Constitution, and while some of them have been filled by amendment, some of them are just ignored and others, like judicial review, are taken care of by judicial fiat.