The man was taken into custody inside the State Capitol on Wednesday after asking to see Gov. Tony Evers, the authorities said. He posted bail and returned hours later with a rifle.
The suspect, Leo F. Burt, has evaded capture since the anti-Vietnam War bombing at the University of Wisconsin, which was considered the largest act of domestic terrorism at the time.
In Wisconsin, Michigan and other states, abortion bans that were long considered dormant could determine if access to the procedure survives the overturning of Roe.