Greenwald, who has published leaked documents from Snowden, was asked by MSNBC host Kristen Welker whether he has been too supportive of the NSA leaker.
"I think that's ludicrous, that's what I say to that," Greenwald said. "Every journalist has an agenda. We're on MSNBC now, where close to 24 hours a day the agenda of President Obama [is] promoted, defended, glorified, and the agenda of the Republican Party is undermined."
Welker defended MSNBC and said the comparison was unrelated to the central issue, which she said was whether Greenwald "crossed the line" while defending Snowden.
"I do defend him, just like people on MSNBC defend President Obama and his officials and Democratic Party leaders 24 hours a day," Greenwald said. "I don't make any bones about the fact that I consider what Edward Snowden did to be quite heroic."