That's a common misconception. Even if you work in "at-will" state, you still have wrongful termination protections. These include both discrimination cases and what are called "public policy" exceptions, which protect employees from being fired over a variety of things ranging from volunteer firefighter service to political affiliation. Employers are also not allowed to fire you for "exercising a statutory or constitutional right" (even in an at-will state). Taking it further, eleven states are nominally at-will but have adopted what's called a "Convenent of Good Faith and Fair Dealing" - which strictly limit the reasons an employee can be fired.

So what does "at will" actually mean? From an employee's standpoint, it means you can leave whenever you want. From an employer's standpoint, it really doesn't mean much of anything.

Even in your coal company example, notice how the CEO was careful to blame his layoffs on a "war on coal" rather then the election result directly? He's throwing Obama's name into it because his horse lost and he's pitching a hissyfit, but the real reason he's laying people off is because coal is not as profitable as it used to be. Romney being elected wouldn't have changed that (if coal is on Romney's priority list at all, it's somewhere around number 9,875,673). That's my point - these "political layoffs" are all bluster. They would've happened one way or the other anyway.