This is a use of "soft power" that differs from the usual definition, ie diplomacy, sanctions etc. as an alternative to armed conflict. What they are really talking about is plain old propaganda and public relations.
It can be decisive. The US got run out of VietNam by propaganda, where militarily we held all the cards. But a bunch of skeevy a-holes in the streets together with complicit media trumped our aces.
getting old.
Nam wasn't lost until the watergate break-in. The propaganda war was not lost - McGovern was crushed in a landslide. Nor was the war on the ground lost - the Easter offensive was crushed by bombing. The US had a win on a platter but the left didn't want it, and after watergate there was no one around to stop them, anymore.