Democrats lined up with Republicans in the 90-6 vote that came on the heels of a similar move a week ago in the House, underscoring widespread apprehension among Obama's congressional allies over voters' strong feelings about bringing detainees to the U.S. from the prison in Cuba.
While the power of the executive order seems broad, there are checks. One check is Congress's ability to overturn executive orders, much in the same way that it may overturn a presidential veto. A two-thirds vote of both houses (i.e., both the Senate and the House of Representatives) is required to overturn an executive order. This means that it can be extremely hard to overturn an executive order, since most members of Congress typically vote along party lines.
When the president of the United States (POTUS) uses a presidential veto, it doesn't necessarily mean that the bill won't become a law. The US Constitution gives Congress a means to sign a bill into law after a presidential veto has occurred. In order to overturn a presidential veto, both houses in Congress must vote to approve the bill by a two-thirds majority. In cases where a majority votes does not occur, bipartisanship — the act of finding common ground via compromise — can help override the veto by gaining a majority vote. Other alternatives include declaring a law as unconstitutional or ruling against same party affiliation.