Democratic presidential candidate Sen. Elizabeth Warren said Friday that she would take steps to break apart Google, Facebook and Amazon if elected.

Why it matters: It's the most significant tech policy idea proposed on the presidential campaign trail so far, and in keeping with a moment where policymakers of both parties have grown skeptical of the power of big web platforms.

Details: The Massachusetts senator's plan involves two key steps.

Get legislation passed making it illegal for companies with over $25 billion in worldwide revenue to act as both operators and users of a platform.

making it illegal for companies with over $25 billion in worldwide revenue to act as both operators and users of a platform. Amazon, for example, couldn't sell its private-label products — like AmazonBasics batteries — that compete with third-party merchants on its Marketplace platform. Aspects of Google's ad and search platforms would be split apart, too, she said in a post.

Install regulators willing to go back and break up already-closed mergers.

willing to go back and break up already-closed mergers. On the list: Amazon's purchases of Whole Foods and Zappos. Google's purchases of ad product DoubleClick, Waze and Nest. Facebook's acquisitions of WhatsApp and Instagram.

Yes, but: Even if elected, nothing's a sure thing. A President Warren couldn't take these steps without some level of congressional support, since one of her proposals requires passing a law and major antitrust regulators require Senate confirmation.

The big picture: This proposal is a boon for a growing anti-monopoly movement that critics have derisively called "hipster antitrust."