This breaks a nearly eleven month string in which Obama has consistently led in the RCPAOP. The last time Obama did not lead Romney in a head-to-head match up in that barometer was October 11, 2011, when Romney led Obama 45,9% to 45.3%.
I expect that Romney will nudge slightly ahead in the coming days with Obama nudging back ahead when the post-Democratic National Convention polls start coming in.
When you look more closely at some of the other questions in the national polls, one thing becomes apparent is that Romney's selection of Congressman Paul Ryan as his VP choice was a shot in the arm for a campaign lacking in enthusiasm, in particular among the conservative base of the Republican Party.
That enthusiasm doesn't affect the head-to-head numbers much, but it is critically important when it comes to turnout. Until Ryan, the motivation for conservative Republicans to vote for Romney was basically limited to casting a vote against Obama. That's not nearly as strong a motivation as giving conservatives a reason to vote for Romney, namely that he has "Ryan" next to his name.