Although a handful of states have some protections around political speech in the workplace, Prevailing opinion from employment law experts is that employees don't inherently have the right to express their political views in the workplace as they do in a broader context. To put it another way, your right to free speech doesn't inherently extend into the context of your workplace. So, while you said,
I mean, he is infringing on my first amendment, I think
that's not inherently true. Further, you said,
at least he is probably breaking some kind of rule to not touch others stuff.
It'a interesting to bring up the idea that someone is breaking the rules here, because many companies have strict policies that limit political activities or solicitations at the workplace. These policies often limit things like displaying political posters or political messages at your workstation, and they sometimes even specifically name screen savers or desktop backgrounds. Per the above references, employers are generally allowed to implement these policies.
So, your first step should be to check with your employer. The fact that a different company owns the specific hardware you're using doesn't exempt you from policies that dictate your use of technology while at the workplace. So, if anything, there's a chance that you might be the one breaking a rule, at least in the context of your workplace.
All that said, you are still left with the issue of how to handle another employee interfering with your workstation, regardless of the above. When it comes to conflicts with peers, often the best policy is to address the peer directly. If you can approach your peer with a constructive attitude, you may find that you can come to an agreement. If you approach your peer with an argumentative or "I'm right no matter what" perspective, you will likely just make the conflict worse.
Finally, you asked,
Can I sue the company for a few million dollars?
That's hard to answer, because it's not really clear on what grounds you would file the suit, given the above.