I can’t imagine only 26.6% independents. That is considerably lower than 2008, while the ranks of independents has grown since then.
As has been posted on FR lately, response rates are way down. Only 9% response rate where it had been 38% in 2008 previously.
IMO, pollsters are overplaying their hand this election, and flooding too many people with too many calls, to the point where they have alienated a large segment. The people who do have time are, speculatively, those who lean Democrat.
But, Rasmussen has to assume by the rules of polling science that the people who do answer his calls are still representative of the voting segment, because it is impossible to prove the makeup of people who won’t be polled.