For example, in 2017 I voted for Mélenchon in the first round, abandoning my preferred candidate, because he had a shot at making the second round (there were three candidates basically polling within the margin of error of each other, for a run-off against Macron)

But instead of trying to widen his appeal to the left since then, he has basically persisted in his "populist" gig, with the (arguably virtuous) objective of seducing the electors of the far right. Also, his party/movement follows the Leninist model of "democratic centralism", which has alienated those of his activist base who believe in democracy.

The result is that he has become toxic for most of the left, so there is zero chance of his making the second round this time.

_{It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II}