One of the key jobs of Congress is to provide oversight and scrutiny of the executive branch. The recent revelation of Hillary Clinton using a private email address, rather than a government one, has caused raised eyebrows, largely due the fact that the archiving of private emails is more difficult than if she had used a government email. A special committee in Congress is readying itself to issue subpoenas for further information regarding this issue.
This is a really good example of the ways in which Congress can provide scrutiny of the executive branch, as well as showing the use of a different type of congressional committee (a special committee, rather than a select committee). Finally it is important to underline the key point you should recognise about the powers of Congress – they are almost all reactive. In this case, whatever Congress find, Clinton has already left office as Secretary of State. The most that some may hope is to case aspersions on her presidential hopes but this doesn’t actually demonstrate an effective scrutiny of the executive branch.