Yes, I didn’t get into the details of Roosevelt’s career, and clearly he became president under unique circumstances. But for the 8 years that he was president (1901–1909) he made some impressive achievements- even more impressive given the fact that, as you pointed out, the country hadn’t originally voted for him to be their leader. It’s true that the man was a singular personality and a tour-de-force… but he was also a product of his times, much like Bernie Sanders is (even though they are obviously very different men.)
The point here is that when people scoff at the idea that anyone could take on the corruption in Washington and succeed, Teddy stands as an example of doing just that. It’s not impossible, it just takes the right combination of individual will and populist mandate.