McCain's office told TPMDC that so far, Napolitano's office has not responded to the letter.
Homeland Security spokesperson Matt Chandler told TPMDC that a response to McCain's suggestion will be coming. He said that Napolitano shares McCain's concerns about the cartel violence in northern Mexico, and has already taken action to prevent it from crossing over the border.
Chandler said the DHS has "implemented unprecedented new efforts to crack down on the smuggling of illicit weapons, cash and drugs that fuel ongoing cartel violence" and " is determined to prevent violence from crossing over the border into the United States."
In the letter, McCain says he has supported sending troops to the border in the past.
"Unfortunately that request was rejected by this Administration," he writes. "A year later, in light of the recent incidents and the continued growth of drug violence along the border, I am asking you and the Administration to immediately reconsider your position and send National Guard troops to our southern border region."
But immigration reform advocates -- who once counted McCain as an ally -- say the new call for troops on the border sounds like little more than campaign politics to them.
"All the language he's using is red meat for conservatives," said Gabe Gonzalez, a national director at the Center For Community Change. "He's getting attacks on the right, so he's going right."
Anti-immigration advocates have long called for sealing off the border, which they say will keep undocumented immigrants out. Gonzalez said that "violence is a problem" on the border, but past experience shows that troops won't solve border problems.
In 2006 President Bush sent troops to the border to clamp down on illegal immigration under pressure from the right. Gonzalez said the plan didn't do much good. He said that the pressure on security just led to more people entering the the U.S. through swaths of desert that were unguarded. Many died of dehydration and starvation on the trip.
"The border is too big -- it doesn't work," Gonzalez said. "You don't solve [the immigration problem] with troops on the border."
(Read McCain's full letter here.)