The legislative branch is constantly fighting the executive branch. The founders of the Constitution placed two very important checks within it. The first is the power of the purse, meaning the Congress can defund parts or all of the federal budget limiting the power of the president. Another major check on the executive is the Congressional approval process required for the appointment of federal judges. in addition to these Congress can override a presidential veto with a super majority vote, although that seems impossible given the current political climate.
Currently the legislative is fighting the executive over the funding of planned parenthood. Congress has voted to defund it, but the president has vowed to veto any spending measure which does so. The last Supreme Courtt nominee to be rejected by the Senate was Robert Bork, nominated by Reagan in 1987. This is an example of the checks the legislative has on executive priviledge of appointments.