This is the kind of thing that Republicans need to pay attention to and drill down on.
I suspect that progressive groups around the country are targeting moderate(ish) Democrats from 2018 who lost their seats, so that they do not run again, and instead a more progress (read, more communistic) candidate runs instead.
What's really going on here, though, is that progressive groups do not like Rouda. He is not agressively progressive enough. He is too "moderate", too "go with the flow", too "corporate." Also, he is too "white". The Democratic Party has entrenched systemic racism, and they are not giving it up. Identity politics has become essential to the Democratic Party, since that is their one and only business. White males need not apply, and that includes former Republican Harley Rouda.
This kind of leftwing ravaging may help Michelle Steel in more ways than one. With Rouda forced to veer harder to the left to keep the Democratic base close to him, he will further alienate independent and event squishy Republicans who have now gone all ga-ga for Biden.
Steel might be able to stay in Congress for another term!