Leo Varadkar is in Washington, DC today for early St Patrick’s Day celebrations. The Irish taoiseach (prime minister) will have breakfast with Mike Pence, the Irish-American vice-president, and lunch on Capitol Hill with President Donald Trump, Mr Pence and the congressional leaders of both parties. He will proceed to the Oval Office, to present Mr Trump and his wife Melania with the traditional bowl of shamrocks—and bend the president’s ear about Brexit. Mr Varadkar fears a future British-American free-trade agreement could lead to a harder border between Northern Ireland and the republic. A powerful bipartisan Irish-American lobby shares his concern. Ahead of his visit, a group of over 20 congressmen wrote to Theresa May warning that the putative British-American deal could be delayed “indefinitely” as a result. “Support for the Republic of Ireland and for a continued peace in Northern Ireland is strong and heartfelt in the US Congress,” they wrote.