Only about one third of US troops will remain
Actually, no doubt less than a third of US troops will remain as there are more than 5,200 US troops in Iraq at present. 5,200 troops was the most allowed under an Iraqi US agreement. However, the US has not kept public figures on levels for months. Although it has added more troops the official number has remained at 5,200.
Pentagon has yet to comment on the drawdown
In Afghanistan the drawdown was happening for months before the Pentagon even confirmed that the withdrawal was taking place or that there had been an order to withdraw troops. So far the same type of situation seems to be unfolding in Iraq.
Trump’s announcement
Earlier in August Trump had announced the withdrawal while meeting with the Iraqi premier. The expectation is that he would carry out the withdrawal before the US presidential election this November. At the time officials did not confirm the totals of the cut.
Justification of the US troop reduction
The main purpose of the US deployment in Iraq has been to help defeat the Islamic State (ISIS). However, ISIS is now barely functioning having lost control of all the territory it once held. US military officials have pointed out that the Iraqi military has the ability now to carry out independent operations against the remnants of ISIS.
There is really no need for the US to stay in Iraq to help fight ISIS. However, the US probably wants to keep a significant presence in Iraq to counter Iranian influence. Some time ago the Iraqi parliament passed a motion to have all foreign troops withdraw from the country but there are no signs that the US is going to withdraw all of its troops. The US threatened sanctions against Iraq should it force the US to withdraw all its troops.