Who's the leader...

...of the Republican Party, Mitt Romney? That's what I would have guessed. After all, he is the party's presumptive nominee for president. But Jonathan Chait, writing in New York Magazine, suggests it's someone else entirely (my emphasis): 

“Now, we are truly at an inflection point, between the Barack Obama and Paul Ryan approaches to government,” National Review editor Rich Lowry wrote recently, treating the elevation of the chairman of the House Budget Committee over the presidential nominee as his party’s standard-bearer as so obvious it requires no explanation. “We don’t need a president to tell us in what direction to go. We know what direction to go. We want the Ryan budget,” says anti-tax enforcer Grover Norquist. “Pick a Republican with enough working digits to handle a pen to become president of the United States.” In any case, Romney has shown no inclination to challenge Ryan, praising him fulsomely and even promising him, according to The Weekly Standard's Stephen Hayes, he’d enact Ryan’s plan in the first 100 days. Republicans envision an administration in which Romney has relegated himself to a kind of head-of-state role, at least domestically, with Ryan as the actual head of government.