I might do a thread on this later, but for now, let me point out that all electoral fraud is not the same. There is pre-election fraud, election-day fraud, and post-election fraud. The last of the three is most brazen and this is what the Trump administration is attempting.

Here are the basics. Different types of governments focus on different types of electoral fraud. The consequences, especially on election results, are also very different. Some help the incumbents by a few percent. Others hand victory to the incumbent regardless of the results.

Pre-election fraud makes it harder for the opposition to run for office or places it at a massive disadvantage during the election. In the US, that includes closing polling stations in opposition areas, unregistering opposition voters, voter ID laws, and gerrymandering.

In more extreme cases, it could entail keeping government critics from even running for office (Iran) or making it very difficult for voters to know who's running against the incumbents through direct or indirect government control over the media (Russia, Hungary).

Election-day fraud includes tactics like ballot-stuffing (Russia), bribery of voters (Kyrgyzstan), voter intimidation (eastern Turkey), and carousel voting (Russia). These usually have a limited impact, though ballot-stuffing can be extremely effective in low turnout elections.

The effect of post-election fraud, unlike the other types, has no limits. The incumbent can simply claim they won. Or put up a bogus vote tally. Or change election laws. These are so egregious and so obvious that you only see it all-out dictatorships (Belarus, Turkmenistan, DPR).

With other kinds of electoral fraud (except when candidates are banned), the opposition can at least hope to overcome an unlevel playing field through record turnout or convincing some gov't opponents to defect. If fraud helps the gov't 5%, they can try to gain an extra 6%.

When the incumbents can ignore agreed-upon election rules (imagine if Dem. legislatures in 2016 argued Clinton won because of the popular vote) and proclaim themselves victors with no evidence of actually winning, elections become pointless. There is no magic number to overcome.

If the state legislature of even a single state gets away with ignoring election results and appoints any electors they want, then democracy in America is dead. It wouldn't even be an electoral autocracy. In the latter, the opposition at least has a chance of winning elections.

If they get away with it, we can simply assume that the heavily gerrymandered GOP-dominated legislatures in most states will appoint GOP electors regardless of the election results. Once certification of ballots becomes a political exercise, they can refuse to certify any result.

Many (most?) of the world's dictators do not engage in post-election fraud. It would ensure that elections become pointless. Even dictators see the value in elections. There is no overcoming post-election fraud. Political change can only occur through extra-constitutional means.