In my opinion, President Obama is seeking Congressional approval for taking action against the Syrian Government because he is concerned about Impeachment. As we all know, Republicans have been looking for an excuse to Impeach him probably from day one. Were Obama to attack Syria in some way without Congressional approval or backing, it would give Republicans exactly the cause they seek to draft Articles of Impeachment against him. You see, any action against Syria without a U.N. sanction is a violation of the U.S. Constitution.
Article VI of the Constitution states:
This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any state to the Contrary notwithstanding.
This violation of the Constitution would clearly be Impeachable in the view of a Republican and perhaps
others as well.
At this point, I would not be surprised to see Republicans work overtime to defeat the Resolution just to challenge President Obama to take action regardless that would, in the end, be Impeachable.