On several occasions in October, Donald Trump tweeted links to stories at Prntly.com, a blog that didn’t exist during the last election cycle. One story (now offline but copied here) indicated that Trump’s support from blue-collar workers was the highest since Franklin Roosevelt in the 1930s. Prntly popped up again last week as the source of a rumor about the Ted Cruz campaign. The site cut and pasted an old story about Cruz’s campaign manager, Jeff Roe. The headline suggested that perhaps Roe had approved the ad attacking Melania Trump run by an anti-Trump super PAC, but it offered no evidence...