Ian Bremmer is president of Eurasia Group and GZERO Media. The opinions expressed in this commentary are his own.

Leave aside the particulars of this month's Brexit drama — Theresa May's dance moves, Boris Johnson's attacks on May's plan, and the latest warnings from European capitals — it's time to brace for Brexit. Let's focus on the few geopolitical certainties we know will follow the UK's exit from the European Union, on whatever terms it comes.

Start across the Atlantic. Brexit won't do the "special relationship" between the US and Europe any favors. An EU without the UK is a much weaker partner for Washington when US-EU interests align and a much weaker foil when those interests collide.

Yes, many of the issues currently dividing the US from Europe have been a long time coming — differences over Russia policy, NATO funding and Middle East adventurism have strained US-European relations before. But Brexit undermines the transatlantic alliance across the board because Brexit challenges will divert Brussels' overall energy and attention away from working with Washington to help bridge their divides.

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The UK will be weaker, as well, in a post-Brexit world. It will need its partnership with the US more than ever, especially as London's standing as a global banking center diminishes. If there's one person who understands leverage, it's US President Donald Trump, who will have a lot more negotiating leverage with the UK when it comes time to negotiate a one-on-one trade deal.

This contrasts directly with the economic message that "Leave" campaigners pushed in the runup to the Brexit referendum in June 2016. According to the Brexiteers, a UK unshackled from Brussels would give Downing Street more freedom to pursue new commercial ties with a broadly diversified set of partners, including rising China.

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