WASHINGTON (AP) — President Donald Trump, the historically prolific tweeter of political barbs and blasts, threatened social media companies with new regulation or even shuttering on Wednesday after Twitter added fact checks to two of his tweets. He turned to his Twitter account – where else? -- to tweet his threats.

The president can't unilaterally regulate or close the companies, and any effort would likely require action by Congress. His administration has shelved a proposed executive order empowering the Federal Communications Commission to regulate technology companies, citing concerns it...