It's really not a pendulum. Some writer pointed out months ago that generally, S. America is splitting into western pro-U.S. and eastern anti-U.S. halves.
There are pendulum effects in most South American countries, and often in South America as a whole. Over the last few decades, on the whole South America seemed to be democratizing. But there has been a return to leftist dictators in several countries in recent years. I would add Evo Morales to the list, and there is now talk that the Sandinistas may make a return to power in Nicaragua.
None of this is Bush's fault, except perhaps the failure to help Ecuadorans remove Chavez in that coup a few years back. It's just the nature of Latin American politics.