From lawsuit after lawsuit. Investigation after investigation. Audit after audit.
As was already pointed out....that's not a source.
This is from your link on the Heritage Foundation:
Claims that the database contains almost 1,100 proven instances of voter fraud are grossly exaggerated and devoid of context, according to
Heritage Fraud Database: An Assessment. It confirms what numerous studies have consistently shown: Voter fraud is vanishingly rare, and impersonating a voter at the polls is less common a phenomenon than being struck by lightning.
“The database includes an assortment of cases, many unrelated or tangentially related, going back decades, with only a handful pertaining to non-citizens voting or impersonation at the polls,” writes the author. “They add up to a molecular fraction of the total votes cast nationwide. Inadvertently, the Heritage Foundation’s database undermines its claim of widespread voter fraud.
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Which clearly indicates that there are instances where voter fraud has occurred. Just not at the rate the Heritage Foundation claims.
It's interesting they don't give actual numbers. Given the number of votes at the poll and the instances of being struck by lightning, I can see why they might use this to hide what could be substantial numbers. Why not just provide them? I know, I know.....I can ask them. Because you won't. You'll just take it at face value.