From The New York Times's article:
The vice chairman and day-to-day leader of the Presidential Advisory Commission on Voter Integrity, Kris Kobach, had asked election officials in a letter to turn over the data “if publicly available,” apparently to aid a nationwide search for evidence of election irregularities. Besides election information like voters’ names and party affiliations, the commission sought personal information including birth dates, felony conviction records, voting histories for the past decade and the last four digits of all voters’ Social Security numbers.
But guess what? Kobach's claims are bullshit. He has claimed there was widespread voter fraud in Kansas, but "he has found scant evidence of it so far."