"Congress has two executive powers: First, the Senate must confirm (approve) any Presidential appointments by a majority vote. Second, the Senate is required to confirm all treaties by a two-thirds vote.".
While it is called executive powers it is in fact part of the built in checks and balances that the constitution provides. While almost all Presidential appointees are usually eventually confirmed, in recent year that confirmation of a Supreme Court Justice has been a contentious issue that has often split the Congess on party lines.