[jpsb]

19% of 49 million voters = 9.3 million (R voters)
14% of 49 million voters = 6.9 million (D voters, Trump won)
11% of 49 million voters = 5.4 million (I voters)
21.6 million (total voters)

Ds, Rs and I’s are approximately equal at 1/3 of all voters so 49 million voters in each group. I added Trumps 74 million and Biden’s 73 million to get a total of 147 million voters and divided that by 3 to get the size of each group (49 million).

[semimojo]

A bigger issue is Bedard is ignoring Rasmussen's likely voter screen, which is always the wild card in their polls.

How are they deciding who's likely to vote in 2024?

You can't extrapolate like this from a population you can't define.