Why would Republicans sign onto the democratic bill in the first place?

This bill seriously helps the Dems chances of retaining the senate and house. It very popular with the majority of Americans. If you look at how things have been progressing so far, the Dems are looking pretty good.

The one flaw that needs to be addressed is what's happening at the border... That is what the Republicans will campaign on. It seems to me that there is always a border crisis or caravan exactly when republicans need it. WTF do they work for republicans or something?