Twitter has no monopoly on the truth. Its fact-check is in need of a fact check itself because it is demonstrably false. There are cases of voter fraud with mail-ins. An election in North Carolina last year was overturned by a court which ruled significant voter fraud was committed with mail-in ballots by Republicans.
Twitter is arguing an opinion, not citing an uncontestable fact. Because it is attacking the opinion of a political candidate, Twitter is interfering with the political process. It should be made to file with the Federal Election Commission. Trump could also declare Twitter is spreading falsehoods in its so-called fact-checks. Would he then be justified sending in Federal officers to pre-approve Twitter fact checks? The question is how we stop powerful social media from spreading lies and distorting the political process.