Article XV
Go read the ABM Treaty text, specifically Article XV:
"Article XV
1. This Treaty shall be of unlimited duration.
2. Each Party shall, in exercising its national sovereignty, have the right to withdraw from thisTreaty if it decides that extraordinary events related to the subject matter of this Treaty have jeopardized its supreme interests. It shall give notice of its decision to the other Party six months prior to withdrawal from the Treaty. Such notice shall include a statement of the extraordinary events the notifying Party regards as having jeopardized its supreme interests."
We withdrew from the ABM Treaty in compliance with the terms of Article XV. That's a far cry from saying we're abiding by the treaty while ignoring it.