Boris Johnson’s resignation Thursday heralds significant uncertainty for the UK. It will spark a leadership contest within the Conservative Party and lead to a new Prime Minister in office by October, with a probable early general election.

This is quite a reversal for Johnson. He has proven in the past to be an electoral winner and a brilliant campaigner, as he demonstrated with the 2016 Brexit referendum and 2019 general election. The British Left will see his departure as a major opportunity to retake power.

This is a high-risk moment for the UK. The Left are delighted to see Johnson removed from power, and many in the opposition Labour and Liberal Democrat parties would like to reverse Brexit.

There is a real danger of Brexit being undermined, even reversed, if the Conservatives lose the next election, and the UK ends up being run by a left-wing coalition, including the Scottish National Party (SNP). Even the future of the United Kingdom would be in question if the Conservatives are ousted from power, with a renewed drive for Scottish independence from the SNP.

A Conservative leadership contest can be a game of Russian roulette. There is no guarantee of a strong Prime Minister and committed Brexiteer winning.

There are several impressive potential candidates to be the next Prime Minister, including Foreign Secretary Liz Truss, Home Secretary Priti Patel, and Defence Secretary Ben Wallace. All three would likely be highly effective leaders in Downing Street.

However, there are also candidates on the Left/Center of the Conservative Party who could gain from splits on the Right, and could emerge as the winner. Previous leadership contests have led to John Major, David Cameron and Theresa May winning. All proved to be weak and ineffective at home, and bad for British leadership on the world stage.

Whoever does emerge as the new Leader of the Conservative Party will face huge challenges, including dealing with a major cost of living crisis, soaring inflation, and Europe’s biggest war since World War Two, in Ukraine, with the threat of further aggression from Moscow against NATO allies including the Baltic States and Poland.

Britain’s new Prime Minister must adopt Thatcherite policies, and run a British Government that is fully committed to advancing a low-tax, limited-government agenda with a clear conservative set of principles. He or she must also demonstrate robust British leadership in the Brexit era, and ensure that Brexit is fully implemented, including through a trade deal with the United States.

The UK must be a powerful force for economic freedom on the world stage, and a vital partner with the U.S. in leading the transatlantic alliance in facing an array of threats, including Communist China, Putin’s Russia, and the Iranian terrorist regime. The world is a far safer and better place if Great Britain plays a prominent leadership role alongside the United States.

Boris Johnson has been a champion of the Special Relationship. His successor must advance the same approach to the most powerful bilateral partnership of modern times.