Sadly, in today's environment there's simply no chance they will be held accountable since most in Ted Cruz's party vote for their party regardless of absolutely anything (and most Democrats are like this too but in my experience that somewhat less loyal to their party).

In other words, none of Ted Cruz's voters are going to vote for the Democrat because Cruz didn't do anything on the border--or even if he broke every single other promise he ever made to his voters--because they've been trained to hate Democrats so much.

We're in a weird political world now where only negative campaigning matters anymore. It doesn't matter to the voter what their candidate does if they are convinced the other side is so terrible.

This is why Trump has recently ordered his party to refuse to vote on border legislation: he knows that his voters don't actually care about the border, they only care about what Trump says. And Biden would get a marginal boost for signing a compromise bill that actually improved things at the US border, and the top priority for the party is to get Trump elected in November, so Trump is against it.

We're in a very, very different realm of politics now, and you need to adjust your brain a lot to understand it. None of the old rules apply anymore .