A federal judge in Massachusetts has stopped President Trump's plan to change US elections. The judge agreed with a group of Democratic state attorneys general who said Trump's action was against the Constitution. Trump's order, given in March, wanted people to show proof of citizenship to register to vote, only accept mailed ballots that arrived by Election Day, and give federal election money to states only if they followed this new rule. The White House said the order would make sure elections were "free, fair, and honest." However, Judge Denise J. Casper decided that the states would probably win their legal cases. She said the Constitution does not give the President special powers over elections. The ruling also stopped a part of the order that required states to reject any mail-in or absentee ballots received after Election Day. This is the second time Trump's election order has faced a legal issue, as a judge in Washington D.C. had previously stopped some parts of it.