So how long have the Republicans griped about the border.

https://theweek.com/politics/house-republicans-immigration-reform-trump-biden

And now they have Biden right where they want him.

He wants a border deal.

They can extract all sorts of concessions from him right now and get fairly close to what they want.

But why do they not do that?

Simply because it is bad presidential politics. Let this be a lesson on why partisan politics suck. The sides say they believe something such as the Republicans saying they want to strengthen the border. But in reality, winning the next election is all they really care about.