Immediate post first round polls indicate Melenchon’s support will transfer to Macron at somewhere between 51 and 62%, with Le Pen getting between 9 and 22% of it.
Projected abstentions among Melenchon voters are currently running at 23 to 36%.
Le Pen will need to drive this abstention rate up as high as possible but even still, I just don’t see where she gets near the amount of votes she needs, as all other main candidates’ support looks like it will transfer to Macron in considerably higher numbers.
Michigan was the primary that Sanders won unexpectedly. Obviously given that Clinton lost the state by 11k votes in November, any Sanders votes that went to Trump were damaging to her, but the point holds that few Sanders supporters backed Trump - a poll in the last week estimated that just 8% would do so.