We all know his seemingly antagonistic act toward Russia really is just an act. Trump is pulling out of the treaty because Putin wants him to.
Obama warned Russia on their suspected violations of the INF in 2015, but did not take any action. "We've" known about this for years.
But what's happening now is Putin has manipulated Trump into withdrawing the US from the treaty, because that gives Putin/Russia carte blanche to develop all the intermediate-range nuclear weapons he wants to. Which, coincidentally, are ground-based weapons with a range of 500 to 5500 km, which are enough to reach Europe, but not the US.
And Trump has already questioned the value of NATO, so is it a guarantee that the US will retaliate/help defend if Russia attacks Europe?
Putin is setting the stage.