Re: 50 cases in the last 25 years
"... it surely reflects poor detection rather than the actual level of fraud."
Not necessarily. Fraudulent voting would mean much more in local elections than in national elections. With the exception - possibly - of California, the states with the highest numbers of "illegals" all voted for Trump. By and large, they have better things to with their time than trying to alter an election outcome. Beside which, when you look at the demographics of the 2016 election, it appears that "liberal" - in the US sense - basically stayed home or refused to vote for Clinton. Not getting Bernie, they apparently said "**** it" and either didn't vote for president or didn't vote at all. Also, as the Democratic campaign demonstrated, it is far easier to rig voting rules in the primaries than in the actual election. The Dems did precisely that and lost. Apparently, the Republicans were nearly as bad. I know many and less than half will admit casting a vote for president. They walked into the polls, voted on the issues that were important to them, but could not choke down voting for Trump or crossing party lines and voting for Clinton.
Fraudulent votes are important in things like city council elections, venues where the out comes are of trivial significance except locally.