WASHINGTON — Maybe it was always going to end this way, with two billionaires angrily posting about each other on social media, fingers flying across pocket-sized screens as their incandescent feud burned hotter by the minute.

What You Need To Know • Insiders have speculated about a potential falling-out between Donald Trump and Elon Musk for months • It never seemed to happen — until Thursday • The world's most powerful man and its wealthiest began attacking each other in a spectacle that left Washington breathless • The feud began with Musk's criticism of Trump's legislative agenda, which would increase the deficit while eliminating tax incentives that have helped his electric automaker Tesla • Trump responded by threatening to cut government subsidies and contracts for Musk's

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