President Trump in speech of December 2, 2020:
Most Americans would be shocked to learn no state in the country verifies citizenship as a condition for voting in federal elections. This is a national disgrace. No other advanced country conducts elections this way.
Many European countries have instituted major restrictions on mail-in voting specifically because they recognize the nearly unlimited potential for fraud. Out of 42 European nations, all but two prohibit absentee ballots entirely for people who reside inside the country, or else they require those who need absentee ballots to show a very, very powerful ID.The entire speech is available at C-SPAN.
These data are directly from the Crime Prevention Research Center report available here.