The 29th Congressional District falls entirely within the boundaries of Los Angeles County. Tony Cardenas (D) is the incumbent and has held the seat since 2012.
This district shows the following party registration for the three largest political groups (the source is http://www.l2political.com):
In spite of the miniscule amount of Republican voters in this district, we saw a Republican make it to November back in 2018. Here are the 2018 primary results:
Tony Cardenas (D)- 66.7%
Joseph Shammas (D)- 8.1%
Benito Bernal (R)- 17.4%
Angelica Maria Duenas (G)- 6.4%
Juan Rey (NPP)- 1.4%
If you calculate the totals from this election, you will see that 65,318 ballots were cast (a low number compared to other districts). 74.8% of ballots were cast for a Democrat and 17.4% of ballots were cast for a Republican.
The low number of Republicans came back to bite them in the 2020 primary. Angelica Maria Duenas (who ran as a member of the Green Party in 2018) ran as a Democrat and advanced to the November election. Here are the results from the March 3 2020 election:
Tony Cardenas (D)- 58.7%
Angelica Maria Duenas (D)- 22.4%
Michael Guzik (R)- 3.5%
Brian Parras (R)- 15.4%
For this election, we saw 88,760 voters turnout and cast a ballot in this race (a fairly large jump from 2018). 81.1% of voters cast a ballot for a Democrat and 18.9% of voters cast a ballot for a Republican. With two Republicans running, you could have made an argument that they split the vote (which they did); however, even adding their percentage together would not have advanced a Republican to November.
Per the jungle primary rule in California, we will now see a November faceoff between Tony Cardenas (D) and Angelica Maria Duenas (D). Cardenas is the incumbent member of the US House of Representatives. Duenas as an immigrant from Mexico and was a member of the Sun Valley Neighborhood Council.
Party registration comes less into play with an inner-party challenge. This one will come down to name ID and resources. I predict that Tony Cardenas is going to win re-election.