Trump needs a GOP majority in Congress (or at least it will make things easier for him if he has one), but it needs to be on his side. If the House GOP caucus can oust Ryan in the next few days, then Trump can make the case for people to vote GOP with a clear conscience. But without ousting Ryan there`s no way people are going to vote Republican down ticket in large numbers.
The newly registered Trump voters and Trump Democrats will only vote GOP down ticket if they know a GOP Congress will support Trump`s agenda.
No chance Ryan will be ousted before the election, the House is not even back in session until after the election. The members are all home in their local districts, campaigning and whatever.