If there were really so many fraudulent ballots cast, why don't more Republicans have a problem with the House and Senate results?

We don’t see a lot of complaining about the House and Senate results from Trump, Republican politicians, or even rank and file Republican voters. If anything, we see efforts to hurry up the certification of those results. It’s only the presidential election that they are contesting. But why? If the top line votes are questionable, aren’t the down-ballot race votes questionable too? The elections all used the same ballots, after all.