As explained here on MSNBC: https://twitter.com/blanesane1/status/1224351803590041600

So they changed the rules of the Iowa caucus for the first time since 1972, AND ANNOUNCED IT IN JANUARY 2020 according to wikipedia. The changes are that smaller caucuses (so rural ones) now count for more delegates per person than larger caucuses (mostly near colleges, which Bernie did really well in), instead of just basing delegates of the popular vote. In 2016 Bernie did really well in those college caucuses, and they were 41% of the turnout. With the rules changes, they would only account for 32% of the delegates instead.

This is a blatant attempt at hurting Bernies chances and results, because it means that they are transforming Iowa into some sort of an electoral college system, instead of basing it on popular vote, which is exactly the OPPOSITE of what Democrats have been preaching since Trump won 2016 through the electoral college, even though he lost the popular vote by 3 million people. This is disgusting and needs to get called out for the election meddling it is.