President Trump on Wednesday threatened to “strongly regulate” or close down social media platforms if they silence conservative voices, stepping up his criticism after Twitter attached fact-checking context to Mr. Trump’s tweets for the first time on Tuesday. “Republicans feel that Social Media Platforms totally silence conservatives voices. We will strongly regulate, or close them down, before we can ever allow this to happen,” the president said on Twitter. “We saw what they attempted to do, and failed, in 2016. We can’t let a more sophisticated version of that…happen again,” the president said.