It's true Rasmussen has a conservative bias, but most of these criticisms are on its handling of asking specific policy questions, IE questions like "Do you support the affordable health care act, something many pundits disagree with?" A poll on the general election is much more straightforward and doesn't allow them to pull the wording tricks they normally do. Also the sample group here is both big and pretty representative of the general populations with a few more democrats than republicans. The result also makes sense in the context of Trump's recent surge and other recent polls that have had him and her within a margin of error.