There is a certain separation of powers in the US that keeps one branch from being able to control another branch. The legislative branch can't force the executive branch to testify any more than the executive branch can force legislators to testify. Heck, there was an uproar in the house (legislative branch) when the justice department (executive branch) got a search warrant from a judge (judicial branch) in order to search a house member's office for a criminal investigation. The fear was that there might have been work product taken from the office and that would be a breach of the separation of powers. It is a convoluted system at times, but it has served us well over the centuries. If t...

There is a certain separation of powers in the US that keeps one branch from being able to control another branch. The legislative branch can't force the executive branch to testify any more than the executive branch can force legislators to testify. Heck, there was an uproar in the house (legislative branch) when the justice department (executive branch) got a search warrant from a judge (judicial branch) in order to search a house member's office for a criminal investigation. The fear was that there might have been work product taken from the office and that would be a breach of the separation of powers. It is a convoluted system at times, but it has served us well over the centuries. If they really want to force testimony, then they will have to impeach.