Ultimately, the backstop became a “vanguard” in Boris Johnson`s withdrawal agreement, with Northern Ireland having to continue to abide by EU internal market and customs union rules, while the rest of the UK could diverge. This avoided a hard border, but meant goods had to be checked between Britain and Northern Ireland. The backstop is valid until the EU and the UK agree to replace it. Look at a company that wants to raise equity and issue 500 shares. Of the 500, only 400 shares are bought by the public. If the company has not entered into a backstop agreement, it must work with a smaller amount. In July 2019, Theresa May resigned and Boris Johnson became prime minister, with Boris Johnson saying he wanted to replace the Irish backstop as part of the withdrawal agreement.  On the 19th In a letter addressed to the President of the European Council on 7 August, the Prime Minister described the agreement as “undemocratic and incompatible with the sovereignty of the United Kingdom”.  He stressed that it was “incompatible with the final objective desired by the United Kingdom” for its relations with the EU. Its third reason why the backstop is not acceptable is that it could “weaken” the Good Friday Agreement and the peace process in Northern Ireland. Tusk replied that those who opposed the arrangement without “realistic alternatives” supported the restoration of a hard border on the island of Ireland.