The issue of who has sovereign powers is what defines a nation. There can be only one sovereign and in the territory of the US the Constitution defines it. Its head is the Chief Executive, who takes an oath to see that the laws are faithfully executed.
The present occupant of that office seems to think that foreign combatants captured while waging war against the US are persons who are entitled to protections of the Constitution. At the very same time he has allowed agents of other governments to operate on US soil?
At the very least this seems to be a violation of his oath of office. Could it be treasonous grounds for impeachment?
Of course it could. But, ultimately, impeachment is something of a popularity contest in Congress as well as a legal truth-seeking exercise. So, until there's a will, there's no way. If and when there's a will, there will be plenty of ways.