WASHINGTON (AP) — A Democratic senator says he is launching an investigation into changes at the U.S. Postal Service that are causing delays in deliveries across the country. Democrats say the delays will be especially bad because of an expected big volume increase for mail-in ballots ahead of the November election. A plan imposed by Louis DeJoy, a Republican fundraiser who took over the top job at the Postal Service in June, eliminates overtime for hundreds of thousands of postal workers and orders that mail be kept until the next day if distribution centers are running late. Michigan Sen. Gary Peters says delays "are preventing Americans from critical mail on-time, including prescription drugs, business mail and mail-in ballots."