Joe Biden has warned the British government about potentially threatening The Good Friday Agreement ---and they are not impressed.

Several British politicians have responded to Joe Biden, the Democratic nominee for the upcoming US presidential election, after he tweeted on Wednesday that the Good Friday Agreement cannot become "a casualty of Brexit."

The discussion around the Good Friday Agreement in the midst of Brexit comes after UK Prime Minister Boris Johnson introduced the Internal Market Bill, which could potentially upend portions of the already agreed-upon Brexit Withdrawal Agreement. On September 8, the UK's Secretary for Northern Ireland Brandon Lewis said the legislation could break international law in a "specific and limited way."

Sir Iain Duncan Smith, the former leader of the conservative Tory Party in the UK, told the UK publication The Times: “We don’t need lectures on the Northern Ireland peace deal from Mr Biden.”

He added: “If I were him I would worry more about the need for a peace deal in the USA to stop the killing and rioting before lecturing other sovereign nations.”

We don’t need lectures on the Northern Ireland peace deal from presidential candidate @JoeBiden. If I were him I would worry more about the need for a peace deal in the USA to tackle the killing and rioting before lecturing other sovereign nations...https://t.co/n22YQ3blwh

— Iain Duncan Smith MP (@MPIainDS) September 17, 2020

MP David Davis, who served as the UK's Brexit Secretary from July 2016 - July 2018, also told The Times: “Perhaps Mr Biden should talk to the EU since the only threat of an invisible border in Ireland would be if they insisted on levying tariffs.”

Biden’s tweet on Wednesday was in response to a bipartisan letter signed by US Representatives Eliot Engel, Richie Neal, William R. Keating, and Peter T. King to UK Prime Minister Boris Johnson which said that the Good Friday Agreement, of which the US is a guarantor, must be protected throughout Brexit. If it is not, a US-UK trade deal after Brexit will be unlikely.

When one commenter replied saying that Biden may be trying to appeal to the "Irish Republican vote," conservative MP Joy Morrissey, who was born and raised in the US, said "clearly it's all about the Irish American vote:"

Clearly it's all about the Irish American vote pic.twitter.com/JfhFxfZ9NZ

— Joy Morrissey MP (@joymorrissey) September 17, 2020

MP Conor Burns,  who served as the UK Minister for Trade from July 2019 - May 2020 and Parliamentary Private Secretary (PPS) to the Secretary of State for Northern Ireland between 2010 and 2012, also tweeted: “Hey Joe Biden, would you like to discuss the Good Friday agreement? It is also called the Belfast Agreement so it doesn’t offend both traditions. Did you actually know that? I was born in NI and I’m a Catholic and a Unionist. Here if you need help.”

Hey @joebiden would you like to discuss the Good Friday agreement? It is also called the Belfast Agreement so it doesn't offend both traditions. Did you actually know that? I was born in NI and I'm a Catholic and a Unionist. Here if you need help.

— Conor Burns (@ConorBurnsUK) September 16, 2020

On Thursday, when asked to respond to Biden's tweet, a spokesperson for Downing Street said: "We continue to remain absolutely committed to no hard border and no border infrastructure between the Republic of Ireland and Northern Ireland.

"And we will continue to engage with our US partners on a bipartisan basis to ensure that our positions are understood."

Asked if Biden was wrong, the spokesman responded: "We will continue to work with our US partners to ensure our position is understood, but the whole point of this - as the prime minister has set out - is to make sure the Belfast/Good Friday Agreement is upheld."