James K Polk is one of the historical figures that is really hard to judge by modern standards.
He was a forceful man with strongly held beliefs. He was the last in the line of "Jacksonian Presidents" with all of the baggage that came along with that.
Ultimately, he was a strong war time President. His single term in office led to the short lived Presidency of Zachary Taylor, who was significantly less informed and forceful than Polk. After Polk, the issue of slavery really came to the forefront. Polk was either responsible for delaying the prominence of this issue or just got lucky. It is likely that history would look much differently if Polk had a second term and continued his aggressive posture towards America's future.
I'd say he was a good President, for his time, who strongly acted on the economy and in regards to Mexico but whose record looks abysmal by modern standards and values.
