The Wall Street Journal reports that with the retirement of Rush Holt, there are very few scientists (or at least people with science PhDs) left in Congress. In fact, Bill Foster, a particle physicist who represents some Chicago suburbs, is the only member of Congress with a PhD in the natural sciences. The article mentions another representative, Jerry McNerney of California, but his Wikipedia bio says that his PhD is in math, which is not science.
I would guess that there are at most a few hundred thousand PhDs in the natural sciences in the US (you can find statistics on recent graduates here – for what I would call “natural sciences” there are around 13,000 graduates per year, many of whom are non-citizens who don’t end up staying in the US), so even having one in Congress is technically an overrepresentation compared to the general population.
However, this does bring up the larger question of who should be representing us. We probably want all of our representatives in the federal government to be highly educated and it would also be useful for them to collectively have expertise in a broad range of fields given the varied responsibilities of the government. While scientists only make up a small fraction of Americans, they do make up a large fraction of people with technical expertise in a number of fields. You can find many sites summarizing the education credentials of Congresspeople (though none for the new Congress yet). It looks like typically nearly all representatives and senators have at least a bachelor’s degree and a large majority also hold graduate degrees, which is good. However, it seems that the graduate degrees are mostly law degrees and MBAs, which means that just two fields dominate the political landscape of the US. That is not to say that no other field has any significant representation, just that those two are so massively represented that they likely often represent a significant majority of Congresspeople. Given that Congress’s main job is to write laws, one would expect people with legal expertise to be significantly overrepresented, but it would probably be nice to see more people from professions and backgrounds outside law, politics, and management (not just science – a Congress made primarily of lawyers, professional politicians, business managers, and scientists won’t necessarily do any better at a lot of issues).
The WSJ article mentions a number of issues that arise in trying to diversify Congress. There are structural issues – people such as scientists often lack the political connections and money required to mount a successful campaign – and also personal issues – many scientists will be loath to abandon their scientific career for politics.