By the way Rochard...I'm not sure where you are getting that "4,000" number from.
The Pentagon is no longer releasing any numbers on U.S. troops in Iraq as part of Secretary Of Defense Mattis strategy of keeping the enemy uninformed.
The Pentagon is no longer disclosing how many troops are in Iraq/Syria - Business Insider
And the numbers were close to 5,000 when the Obama administration was openly putting out that information in late 2016.
Mattis doesn't allow our enemies to see what our plans are now...but all reports coming in from Iraq indicate a much bigger U.S. presence in the fight (which is why ISIS is suddenly losing so badly).