.., he was not a "mixer" socially, not, anyway, with most members of Congress and their wives. His manners were impeccable, his charm impelling, but he kept his social life distinct from his official life and congressmen were rarely in his social circle. To know how Congress works but to disdain its joys is an acquired taste for most ex-congressmen downtown, produced by hard experience. Kennedy, however, brought it with him. Many of the difficulties he was to encounter in his day-to-day congressional relations stemmed from that disdain (p. 174, 1990 edition).
Sound familiar? This judgment, too, seems all the more apropos for our current president, faced as he is with an opposition, in control of the House and able to block all action in the Senate, determined to stymie his every initiative:
But even if he had been a man who dearly loved the Congress, even if that feeling had been reciprocated, nothing could have rendered their relationship sweetness and light in his last year, so long as he persisted with his legislative program. As an innovative President confronting a reluctant Congress, he was heir to Truman, and to Roosevelt after 1936. Kennedy's own manner may have hurt him on the Hill, but these were scratches. Deeper scars had more substantial sources, and he knew it (pp 174-175).
In Obama's case, those "substantial sources" are an opposition willing to sabotage the economy, deny health insurance to tens of millions, and demonize policies they have long and recently supported to assure his failure.
P.S. I put "introvert" in quotes because I don't think the label fits either Obama or Kennedy. Many if not most people are a mix of intro- and extroverted characteristics. I pretty much know that's true of Obama, and I suspect it's true of Kennedy.