Constitutional Crisis

In the recent past, there has been one Constitutional crisis, in which politicians have not been following the rules laid out in the constitution, that has stuck out to me. That crisis happened during the Bush administration in which Bush had been wanting to go to war so bad that he circumvented the Constitutional rules and powers given to Congress of declaring war. He had tried to go through the United Nations to see if they would back the U.S. in a war in Iraq; They denied him. So he goes to Congress asking for the rights to go to war and in return he would have the U.N. back the U.S. in war. Congress understood this to be a sound statement, so they signed off on it; They gave him the power to declare war against Iraq. Bush then, instead of going to the U.N. for backing, went straight to war with Iraq. This to me seems as an infraction of Constitutional powers and rules for each of the three branches of government.