Strategies for a Republican Congress
According to polls, the congressional Republicans are losing. They need a strategy. Here is one. They should use the slogan: "Don't trust anyone".
This would be popular because it matches the national mood. Pew Research reports: "Public trust in government near historic lows"
The main argument should be that Biden is certain to beat Trump, so the voters should protect themselves by electing a Republican Congress. There is evidence that the voters want a Congress of the opposite party from the President. This is mainly true for moderate voters: they want a Congress that balances the President.
To help drive this point home, the Republicans could publicize some Democratic plans. The Democratic House voted to admit the District of Columbia as a State. In 1978 the Congress proposed a Constitutional Amendment to do that. It was rejected overwhemingly by the States: 16 in favor, 34 against. It probably isn't any more popular today. Another example is expanding the Supreme Court. That is also unpopular. In a recent New York Times/Sienna College poll, 31% were in favor, 58% were opposed, and 11% were undecided.
The big problem with this strategy is that it means abandoning Trump. That creates a problem for Republican Senators who depend on Trump voters.
There is another approach. The Arizona Presidential primary resulted in almost a quarter of the votes going to candidates that had already dropped out. That was because Arizona didn't allow voters to change their votes. The Senate could demand that States allow their voters to change their votes. (Some States already allow that.) The Senate could refuse to seat any Senator elected by a close margin where vote changing wasn't allowed. They could demand a revote. Something similar has already happened in North Carolina, where the House required a revote because of fraudulent votes in the 9th District.
Still another approach is to test the integrity of the electoral process. Republicans complain about the possibility of voter fraud. The Democrats point out that there have been extremely few documented cases of actual fraud. (The North Carolina 9th District may be an exception.) But that only tells us how many got caught. So either very few tried to vote illegally, or else it's very easy to get away with. The Attorney General could authorize an attempt at fraudulent voting in some states. To prevent actual corruption of the results, they could all cast a write in vote for a fictitious candidate. The number that got caught and eliminated would tell us how secure the system is.