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Yes, I consider that a significant weakness.
You keep differentiating between the primaries and general, but to quote you above "Yes, well, getting the right votes are part of campaign performance." In the US, part of being a strong candidate means not only winning the Electoral College, but also winning a major party primary prior to that. That is the system.
And yes, I do not have future sight, so I cannot tell you for sure that Trump will be the nominee, but I see no evidence that he's particularly weak in this primary, indictment or no. He's polling well in the lead and I think is up to 10 Senate endorsements and 50-odd house endorsements for whatever those are worth.