This Sunday, when Mexicans will vote for a new president, Bolivians will also be going to the polls — selecting a new constituent assembly that will rewrite their constitution.

Bolivian president Evo Morales is using Venezuelan leader Hugo Chavez’s example as a model to concentrate power. Chavez introduced a new constitution that centralized political control and he has used popular referendums to eliminate checks and balances on his power. Morales will have a somewhat harder time at gaining and maintaining similar control, since he doesn’t have the vast oil resources or military background to support him that Chavez has.

If Mexican populist Andres Manuel Lopez Obrador is elected this weekend, will he too follow the Chavez path? Many observers, including the market, don’t seem overly concerned. Mexico is not Bolivia; it is a much larger, more diverse, open economy with a free trade agreement with the United States. Democratization and economic reforms — especially openness to international capital markets — will temper Lopez Obrador’s populist sentiments. At least, so the argument goes.

Unfortunately, I don’t believe that Mexico’s reforms have been sufficiently institutionalized. Mercantilism, political opportunism, and the party machine are still quite alive in a Mexico that spent most of the 20th century looking inward and under state domination. Even President Vicente Fox’s great achievement of maintaining a macroeconomic stability not seen in more than 30 years depended heavily on the admirable qualities of the current finance minister and central bank president.

As Mexican economist Manuel Suarez Mier has been emphatically warning, a President Lopez Obrador would find it relatively easy to buy off congressmen from the opposition and discredited PRI party and to thus begin re-establishing the political hegemony that existed in Mexico before Fox came to power. Except this time, the ruling party would be Lopez Obrador’s PRD.

That scenario may seem extreme, especially since it would require plenty of resources to sustain. The path to populism in Mexico would be different than that of Venezuela. But given Lopez Obrador’s political record of behaving irresponsibly and openly disdaining the rule of law (e.g., he has disregarded court rulings with which he disagrees), there is every reason to believe that he will follow through with the vast New Deal-type spending projects that he has promised, the creation of state-owned businesses, and the protection of favored industries even in the face of adverse economic results.

Bolivia is guaranteed a rough ride almost regardless of its election results this weekend. Because the leading presidential contenders are essentially tied in the polls, Mexico can still opt against the candidate that promises to take the country backward.