If a Russian agent became President of the USA, I would expect him to disarm american citizens and to reduce the power of the U.S. military.
e: if you're downvoting please explain why.
Weakening the U.S. military sounds like a more worthwile goal. Reducing their budget would be one way to do that, but that's easily undone. I would go for more a more sublte approach to inflict better long-term damage. Try to restructure and reprioritise to get less done with more money. Try to get rid of important military installations abroad. Try to burn bridges with allies to make sure the US military has to take a larger burden in foreign interventions. If you're feeling really bold, try to establish entirely new arms of the military to further decrease effectiveness and increase spending. Try to do all of that in a way that's hard to undo by the next president.
It seems like a no-brainer that an enemy force (Russia in this instance) would want to disarm the people they plan to attack/control.
The OP asked what I'd expect from a Russian Agent as President, and that's what I'd expect one of the first steps to be. I _wouldn't_ expect a russian agent who became president of the U.S. to fight for the 2nd Amendment/arming of citizens and to push for the EU to increase their military spending.
Sure, it could happen, but I wouldn't expect it.