Depending upon the POD when he actually becomes involved in politics he would be the first US President that really went off and saw the world. The US could becomes more un-isolationalist - tho it never was isolationalist - but more involved internationally. American manifest destiny into the Pacific and Asia would have been put off during the duration of his administration. Hawaii would have remained an independent nation since he was fairly anti-imperialist IIRC.
Much like the AH collection of short stories titled 'Alternate Presidents' he would probably be very similar to the Benjamin Franklin character portrayed there. Congress would hate him since he would be 'telling it like it is' to the public. I could easily see him going off on a whistle stop tour of the nation to drum up support for his policies.