I voted last Saturday. In my state voting is by mail and votes are counted by county elections clerks. It is managed honestly, with vote counting observed by political party representatives and the public. All ballot envelopes are opened with observers present, then counted in batches by tabulating machines.
Very recently a temporary elections worker in a neighboring county was caught tampering with ballots, marking them for republican candidates in races that voters had left blank. The county clerk reported that criminal violation of state elections law to the secretary of state's elections division and the state department of justice. That worker has been relieved from duty and is facing prosecution for a felony punishable by imprisonment for up to five years. The ballots that were tampered with were destroyed, the secretary of state has two people monitoring the vote counting in that county elections operation, and the only pens allowed near ballots are bright colors that the vote tabulating machines can't register.
If voting in a particular race is very close, the losing candidate can demand and get a recount by hand.