Melania Trump and Natalie Harp were in very close quarters Sunday ... as both watched the Freedom 250 IndyCar race with President Trump nearby.

Video from the race shows Melania seated right next to POTUS ... while Harp was sitting just a few feet behind the First Couple.

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It's an interesting visual considering all the attention Harp has been getting lately over her close relationship with Trump.

As we reported ... Harp has become a near-constant presence at his side, traveling with him and helping manage his papers and social media.

That closeness has only fueled more questions ... especially after personal letters surfaced in which Harp told Trump he was "all that matters" to her.

Then came the access issue ... a report claimed Harp worked in the White House for more than a year without completing the normal security clearance process.

Not everyone thinks the attention is fair ... Sen. Bernie Moreno told TMZ DC Sunday the scrutiny surrounding Harp is "super misogynistic" ... saying nobody would care if she were a man.

As for the Freedom 250 Grand Prix ... we reported earlier Sunday Trump took credit for helping make the inaugural Washington, D.C. race happen after years of stalled plans.

Plenty of action on the track ... and a pretty interesting seating chart off it.