Factcheck.org:

President Donald Trump wrongly claims that “58,000 non-citizens voted in Texas, with 95,000 non-citizens registered to vote.” This latest voter fraud misinformation from the president is based on the state’s efforts to match driver’s license and state ID card applications from noncitizens to voter registration rolls.

However, the Texas director of elections warns the lists provided to county elections officials represent “WEAK matches” (the capitalization and emphasis is the state’s) and does not account for the possibility that many people on the list may have simply become naturalized citizens after having obtained a driver’s license.

History tells us to be wary of these numbers. In Florida, when officials similarly matched driver’s license and voter registration data in 2012 in an attempt to remove noncitizens from voter rolls, an initial list of more than 180,000 names was ultimately whittled down to less than 100.
Nevertheless, Trump, who has long warned — without evidence — about widespread voter fraud, claimed via Twitter that Texas had found evidence that tens of thousands of noncitizens have voted illegally in U.S. elections. Trump claimed Texas’ discovery was “just the tip of the iceberg” and that “voter fraud is rampant” around the country. It “Must be stopped,” he wrote, with “Strong voter ID!”