Some states have registration by party, but some do not. Some states have early voting for everyone, but some do not.
The data that we're seeing is in the states that have early voting for everyone AND registration by party, we're seeing more registered Republicans voting. This is promising, but it isn't proof of how people are voting. We're also missing the data from the states that don't have registration by party or early voting.
Actual proof doesn't get released until after the polls have closed for those states.
A simpler explanation
Trump wants people to vote early to better ensure that people actually vote. A million and one things could happen to prevent a Trump voter from voting on election day, so it's better to lock in those votes early and not take any chances.
I'm skeptical
Some states have registration by party, but some do not. Some states have early voting for everyone, but some do not.
The data that we're seeing is in the states that have early voting for everyone AND registration by party, we're seeing more registered Republicans voting. This is promising, but it isn't proof of how people are voting. We're also missing the data from the states that don't have registration by party or early voting.
Actual proof doesn't get released until after the polls have closed for those states.
A simpler explanation
Trump wants people to vote early to better ensure that people actually vote. A million and one things could happen to prevent a Trump voter from voting on election day, so it's better to lock in those votes early and not take any chances.