It's BS. Rasmussen has always overinflated Trump support from black voters.
"One week before the 2018 elections, Rasmussen had President Trump's support among black Americans at 40 percent. According to exit polls, only 8 percent of black voters nationwide voted for Republican candidates."
"Gallup averages show Trump with a 10% approval rating among blacks in 2017, 11% in 2018 and 10% so far in 2019."
Another poll in October showed him with just 7% support.
The Emerson Poll, released November 21, indeed showed Trump with 34.5% of black registered voter approval. RedState noted, “Thirty four percent approval for President Donald Trump. And that’s not an outlier with other Rasmussen tallies, the average has actually gone up since last year when it was in the 20s.”