Feckless or reckless?

A writer named Paul Pillar described Jeremy Corbyn as a "feckless left-winger", and a lot of people think that Boris Johnson is too reckless to be Secretary of State for Foreign Affairs. I just realized that "feckless" and "reckless" are different and the difference is just one letter. While I feel that Boris Johnson is a reckless person, I don't know if Jeremy Corbyn is feckless or not. I am interested in the context where the two words are used. Which word is more favored by those who want to criticize their antagonists? To you, which word causes more damage?

I prefer to be called "feckless" rather than to be called "reckless".