On another political issue, McCain said that former Sen. Chuck Hagel had been weakened by his battle to be confirmed as defense secretary, but McCain said he and Senate colleagues could work with Hagel at the Pentagon. Hagel is expected to be confirmed Tuesday after fierce attacks from fellow Republicans including McCain.
"I think he will have been weakened, but having said that, the job that he has is too important," McCain said. "I know that I and my other colleagues, if he's confirmed, and he very likely will be, will do everything we can to work with him."
McCain was defeated by Obama in the 2008 presidential election.
Turning to Mexico, McCain said Pena Nieto had reassured him that Mexico would continue to battle drug cartels while reassessing the country law-enforcement strategy.
The Mexican administration that took office Dec. 1 has, at least in its public rhetoric, emphasized social programs and economic growth as the answer to drug crime, a change from the previous government's focus on a militarized offensive against cartels. That has provoked concern in Washington about a reduction in anti-drug cooperation with Mexico.
"I have no doubt about his commitment," McCain said of Pena Nieto. "I think he feels that policies and practices of the previous administration need to be examined."
McCain said the Mexican president had emphasized the need to reinforce Mexico's southern border with Guatemala, a new emphasis in a relationship that has focused heavily on the U.S.-Mexican border.
The Mexican government said Pena Nieto "emphasized the necessity and the benefits of diversifying the agenda and the dialogue between Mexico and the United States," to focus on economic issues including the automotive industry and educational, scientific and technological cooperation.
Pena Nieto's government is in the midst of an international and domestic public relations campaign to undercut Mexico's association with drug crime and promote its relatively strong economic growth, driven partly by foreign investment in manufacturing plants here.
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