"I mean she's got to do what she's got to do", he said at the White House as he welcomed Irish Prime Minister Leo Varadkar for an early St. Patrick's Day celebration.
'I gave the prime minister my ideas on how to negotiate it and I think you would have been successful.
Prior to the breakfast, Varadkar said differences between their administrations' views on gay rights are clear, but that the two countries have a good working relationship, according to the Independent.
Asked by a reporter if he believes there should be a second public referendum on Brexit in Britain, Trump replied he does not think that would be possible and it would be "unfair to the people who won".
"We have a different opinion, president", said the Irish prime minister. "We're going to tariff a lot of their products coming in because the European Union treats us very, very unfairly", he said.
Mr Varadkar said: "I stand here this morning as leader of my country, flawed and human, but judged by my political actions and not by my sexual orientation or my skin tone or my gender or religious beliefs".
He said he would like to see the "whole situation with Brexit work out", adding "we are talking with them about trade and we can do a very big trade deal with the UK".
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Leo Varadkar also thanked President Trump for his support of a new E3 visa programme which, if passed by Congress, would benefit Irish citizens who wish to work in the US.
Nr Varadkar was speaking at the Ireland Funds dinner in the National Building Museum during his annual St Patrick's Day visit to the US.
Mr Varadkar also said the leaders spoke about the issue of the undocumented Irish in the US.
"It's just a great place", he added.
British parliament on Tuesday overwhelmingly rejected Prime Minister Theresa May's Brexit deal, throwing the country's Brexit process into further chaos. "But I think it could've been negotiated in a different manner, frankly", he said.
Mr Pence made the comments at a breakfast meeting with Mr Varadkar and his partner at the vice-president's residence in the capital.
"I will be coming at some point this year".
At the traditional shamrock presentation at the White House on Thursday evening, Mr Varadkar praised Mr Trump's ambitions to "make America Great Again".