The United States should look at the development of more bases in Eastern Europe to protect against Russian aggression, but rotate forces through them rather than make permanent deployments, the chairman of the Joint Chiefs of Staff told Congress on Tuesday.

Army Gen. Mark Milley said the basing could be funded by other countries such as Poland and the Baltics that want more U.S. troops. Defense Secretary Lloyd Austin said any effort to expand security in Eastern Europe is a “work in progress” that probably will be discussed at the NATO summit in June.