Seems to be a wrong question. 2nd blank should be clearly galvanize.

question is just alright, for your question that "galvanize " cannot be for second blank because we need some word that define intensity and intensity mean fervent.

I don't see anything wrong with the question

It basically reads that there is clear(limpid) support from his backers but that support is not enough, so now he has to galvanise more support for him to be considered a serious threat

in this question:
many of the most means maximum.
So the question says, the fringe party candidate had the clear (limpid) maximum support that he could have, what he needed was more passionate (fervent) support from the people who were already supporting him.

To galvanize support would mean to cause to become active or to gather more support, which is not needed as he already had the max support.