[I]f the Republican leadership is going to insist that sixty votes in the Senate are required to do any business at all in this town, then the responsibility to govern is now yours as well. Just saying no to everything may be good short-term politics, but it’s not leadership.
Obama admits that the Republicans have developed a brilliant political strategy of obstructionism. It has badly hurt Democrats and helped get Republicans elected. After acknowledging that just saying "no" is a very smart move, Obama asks and weirdly expects Republicans to change. Why would they ever give up a working strategy that had enabled them to win a Senate seat in Massachusetts?
This is not an issue of leadership, or just “short-term politics.” Senators are professional politicians. This is their job, their life, and often their passion. Giving up the great political strategy of just saying "no" would endanger their livelihood.
So, when Obama asks Republicans to be bipartisan, he is asking them to make a very bad personal, political, and professional choice. Working with Democrats would require Republicans to give up a working political strategy. It would increase the chance that these same Republican senators would loss their jobs. It would also help Obama and the Democrats look good, more centrist, and very effective. The result of helping Democrats look good would probably be to prolong the amount of time Republicans spend in the minority.
Obama acknowledges that it would be very stupid for Republican to work with Democrats. Even after saying that being bipartisan would put Republican senators' jobs in jeopardy, he honestly expects them to want to work with him.
As long as Republicans have every incentive not to work with Democrats, Democrats must stop chasing bipartisanship. No one should every expect politicians to work against their own re-election to help pass the opposing party's agenda. Until it directly benefits Republican senators to work with Democrats (something that does not appear to happen anytime soon), bipartisanship is logically doomed to fail. Until that happens, the refusal of Democrats to move popular legislation with Republican support plays right into the Republican strategy, and only encourages them to be less cooperative.