Can I ask a stupid question?
How can the federal government or a president, somehow decree free college at state colleges and universities? The states run their colleges and universities. The states decide on levels of tuition for in state residents vs. Out of state.
So is the federal govenrment going to take over state colleges? How the heck will the somehow give free college unless they take over all these state cilleges?
Dilbert.... really. You are THINKING TOO MUCH.
You are obviously unaware of the concept of the Imperial Presidency. Her Majesty will first require the colleges to set their tuition according to her guidelines. If they refuse, no federal dollars for their students. The colleges will play along. Then the federal government will pay that tuition.
This will all be done by regulation, or by executive order. No need to bother Congress.