Presidents Carter and Clinton testified under oath. Bush and Trump didn't dare testify under oath because they lied all the time. Look at it this way. When republicans have power they have hearings that none of us can see.When Dems have power, they have hearings that we can watch and decide for ourselves. This happens over and over. The Bush White House failed on 9/11 and again when it lied about WMDs. Bush and Cheney were questioned but it wasn't under oath and we never saw their answers. Today, it's worse. No one even dares to ask them questions under oath because everyone knows they'll lie.