LAS VEGAS — It’s a picture that’s gone viral on the Internet: Arizona Gov. Jan Brewer (R) pointing a finger at President Obama as they argued on the tarmac in Phoenix on Wednesday.

But why is there no video footage of the heated exchange?

A producer for NBC News, which was serving as the television representative in the press pool that follows Obama aboard Air Force One, said the camera crew captured Obama descending the stairs and shaking Brewer’s hand.

After a few moments of what started out as a routine presidential receiving line, however, the NBC crew, which was lugging a camera and other gear, quickly moved to the next spot Obama was headed to: a rope line where he would shake the hands of residents who had been admitted to welcome him. A White House camera crew also moved to the rope line.

From that vantage point, neither could capture the scene back at the receiving line because their view was obstructed by the president’s bullet-proof limousine, reporters said.

The rest of the press pool — wire service reporters, a radio reporter, a news photographer and a Politico reporter serving as the newspaper representative — stayed behind with the president. That’s when Brewer’s conversation with Obama grew heated.

The NBC producer said she ran over to try to get the crew to return to receiving line, but the president abruptly ended his dispute with Brewer by walking away. Obama then greeted others in the receiving line, before moving to the rope line as planned.

Obama was spotted by one reporter at the scene flinging a letter Brewer had handed him into the limo as he walked toward the rope line crowd.