Pena Nieto left the door open for the PRI to ditch anti-union measures in Calderon's bill, mindful they were divisive.

MSN: Analysis: Mexican labor reform signals battles ahead for Pena Nieto - World news - Americas | NBC News

But the most fearsome of these fences isn't "The Chair, " a 5-foot-3 high hedge fronted by an open ditch, the sharp bend of the "Canal Turn, " or even the dreaded "Becher's Brook, " with its steep 6-foot-5 drop.

WSJ: Why They Fear Aintree's First