Gillibrand was formerly a moderate Democrat while serving as a congresswoman from upstate New York before becoming the progressive 2020 candidate she is today, Steyn said Monday on "Tucker Carlson Tonight."
Steyn added Gillibrand used to hold, "very moderate, centrist views that she's tossed overboard along with her twirling moral compass in the last three months. So, she just comes across as a shallow opportunist."
To that effect, host Brian Kilmeade played several clips of Gillibrand saying the U.S. was "founded on some basic moral principles" and "we have a moral compass as a nation" and "our morality as a country is literally on a knife's edge."
Kilmeade added Gillibrand also recently changed her view of the Clintons -- noting then-Gov. David Paterson originally appointed her to fill Hillary Clinton's U.S. Senate seat in 2009 after the former first lady was nominated secretary of state.
In response, Steyn claimed Gillibrand was "not the same person she was five years ago."
"That gives her a credibility issue and makes her sound fake when she's lecturing audiences... on how they're suffering from white privilege," he added.
"This is just someone who embodies all the worst, most opportunist, most shallow aspects of American politics."