Obama’s Keystone veto is only his third in six years. It won’t be his last.

Obama showed “a genuine reluctance” to use a veto before, according to Princeton University professor Julian E. Zelizer, partly because he was elected on the grounds that he could forge a new political consensus. Even when that goal became elusive, Zelizer added, the president and his aides were aware that any veto gives the GOP fodder to “rally Republicans, and even some moderate Democrats, to be against him.” “I think he’s changed,” Zelizer said. “He’s just adjusted to this being the only tool he has left.”