One of his main problems is that he doesn't know how to keep his mouth shut. He has an almost physiological need to express his opinion about everything and everybody. Venezuelans are already used to having their favorite TV shows interrupted when it occurs to him to say something. Those events, it is worth noting, may last hours.

Every Sunday on his program "Alo Presidente" ("Hello, President"), he forces his ministers and aides to laugh at his jokes and listen to him attentively _ without having a chance to question him _ until he gets tired. And he does not wear out easily. Just like former Mexican President Luis Echeverria, he is known for talking endlessly without even taking a bathroom break, while his ministers squirm in their seats in agony.

And anyone who talks and improvises without interruption and without any kind of filter between the arrival of an idea in his head and its emergence from his mouth, are doomed to make mistakes. That is exactly what has happened recently in Chavez's case.

It's no secret he would like to see Ollanta Humala win Peru's presidential elections on June 4 and Andres Manuel Lopez Obrador win Mexico's elections on July 2. But instead of helping his favorite candidates, his public comments have seriously harmed their standing in opinion polls.

He still hasn't figured out that he strikes fear in the hearts of many Latin Americans. Who wants their country to be ruled by an authoritarian, who never listens, who boorishly insults other leaders and who threatens to stay in office forever?

Let's take a look at Peru. Nationalist candidate Humala handily won the first round of elections there. But as soon as Chavez called Humala's second-round opponent _ former Peruvian President Alan Garcia _ a "thief" and threatened to break off relations with Peru if Garcia wins, Humala began sinking in the polls.

If he had just kept quiet _ like controversial Argentinean soccer star Diego Maradona did in his recent visit to Lima _ it is possible Humala could have avoided the link with "Chavist" extremism. But that wasn't to be.

Humala had to ask him not to concern himself but to leave it to Peruvians to take care of their own thieves. But, the damage was done. A video showing Humala meeting in Caracas with Chavez and new Bolivian President Evo Morales is circulating everywhere. And now Humala will have to work hard to overcome Garcia's lead in the latest polls.

Let's go to Mexico. Lopez Obrador, the candidate from the Democratic Revolution Party (PRD), has never seen Chavez let alone talked to him on the phone. But the Venezuelan leader _ guess what! _ has already opened his mouth to openly support Lopez Obrador.

Aside from that, we must take note of Venezuela's ambassador to Mexico attending a PRD rally _ what was he doing there? _ and Chavez's threatening Mexican President Vicente Fox not to mess with him or "he'll get hurt."

Taking advantage of the situation, candidate Felipe Calderon from the ruling National Action Party (PAN) put out an advertisement in which he compared Chavez famously telling Fox to "shut up, chatterbox" with what Lopez Obrador himself said about the Mexican president. One of Calderon's aides told me the ad was intended to suggest that "Lopez Obrador was as intolerant as Chavez." And it worked.

Arrayed on my desk are the last six surveys carried out in Mexico (by Gea, Consulta Mitofsky, Parametria, Reforma, Milenio and El Universal) in which Felipe Calderon appears with a clear lead over Lopez Obrador, who for months seemed invincible. Lopez Obredor's stumble is due, in part, to his refusing to take part in the first presidential candidates debate.

But aside from campaign mistakes, the Chavez image has really harmed Humala's and Lopez Obrador's presidential aspirations. It is the "black hand" of Latin-American politics, in the face of which Humala and Lopez Obrador can tell him: "Don't give me any assistance, pal."

There's more.

After Evo Morales was elected president in Bolivia, his clear alliance with Chavez and Cuban dictator Fidel Castro, as well as his recent nationalization of the oil and gas industry, has other Latin American countries looking much more carefully at presidential hopefuls from the political left. After achieving a handful of presidencies through elections, has the left reached its limit in Latin America because of Chavez? We will find out soon.

Meanwhile, the lesson for other presidential candidates is the Chavez factor: associating yourself with Chavez can cost you the elections.

If he really wants to see Humala and Lopez Obrador secure their respective victories, the intelligent course would be to keep mum. But that appears impossible. He has an unstoppable tongue, loves to hear his own voice and constantly monopolizes the cameras. Who would dare silence him or snatch away the microphone?