Just what is the US interest in Syria?The situations are hardly comparable. The final US exit didn't resemble the negotiated one.
The question is does the US have an interest in the outcome in Syria or not? If it does, then according to Trump, it's not dependent on a small force of 2000 being in Syria. As criticism grew, Trump implied it could be accomplished thru US forces in Iraq. While Trump had spoken of withdrawal 6 months ago, his order was not the result of consultation with anyone, at least made public or even claimed by the WH or allies. An official act that is in Russia's interest but not the US interest, at least according to Mattis and retired officers that spoke out against Trump's declaration of victory over ISIS.