This morning, the International Space Station commander surpassed the record of 534 days, two hours and 48 minutes for most accumulated time in orbit by an American.
After Whitson described technology to support long-duration manned trips to space - including a system that converts urine to drinking water for astronauts - Trump went off script.
"Five-hundred and thirty-four days and counting. That is really something".
Ms Whitson is also the first woman to command the space station twice and the only woman to have led Nasa's astronaut corps.
Trump used some of his time speaking with Whitson and her fellow crewmember Jack Fischer to talk about the military and the inspiration that space brings to kids watching the long-distance video call around the country. "That's an incredible record to break".
"It is actually a huge honor to break a record like this", Whitson said, thanking her NASA colleagues for making it possible.
Until now, the record-holder, when talking about the USA astronauts, was Jeff Williams with 534 days, 2 hours and 48 minutes of cumulative time in space.
She said, "The kids were really excited about it and very engaged in conversation". While aboard the ISS, she sequenced DNA, an experiment that she said had far-reaching implications in space and on Earth.
"We are absolutely ready to go to Mars", Whitson said, as both she and Fischer raised their hands.
Holding records is not new to Whitson.
Whitson already was the world's most experienced spacewoman and female spacewalker and, at 57, the oldest woman in space.
"What are we learning from having you spending your time up there, I know so much research is done - I'm getting a glimpse of it right here in the Oval Office - what are we learning by being in space?"
NASA astronaut Peggy Whitson on a spacewalk in March 2017.
Whitson, who has a doctorate in biochemistry, is no stranger to breaking records.
They include increasing the effectiveness of chemotherapy drugs for cancer treatment, and growing fresh food in space.
Trump learns about space. The astronaut also called for global cooperation to ensure the success of the scheduled two Mars missions, pointing out the "very expensive endeavor" needs a "planet-wide approach".
Her fellow US astronaut Jack Fisher arrived at the ISS last week for the first time.