The president said: 'I'm surprised at how badly it's all gone from the standpoint of a negotiation.
"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.
Speaking ahead of a private meeting with Mr Varadkar, the United States president said Brexit was "tearing countries apart".
"She's got to do what she's got to do but I think it could have been negotiated in a different manner".
On the prospect of another referendum, he said: "I don't think another vote would be possible because it would be very unfair to the people that won".
"We have a different opinion, president", said the Irish prime minister.
"I am happy to report to the Taoiseach that I have spoken to mom, first generation Irish-American and mother-of-nine, and she has confirmed that she will travel with us to Ireland and we are making plans to return to my grandfather's homestead as we speak", Mr Pence said.
"We talked about Brexit, something that's turning out to be a little more complex than they thought it would be", Trump said at an annual Capitol Hill luncheon for the Irish hosted by the House speaker.
'BOMB CYCLONE': Late-winter storm hits U.S. Midwest after paralyzing Colorado
In the Texas Panhandle, a utility worker was killed while working to restore power amid strong winds pushed in by the storm. Five people were hurt and 150 dairy cows had to be euthanized when a tornado hit the small town of Dexter, New Mexico.
Christchurch attacker meant to continue rampage when arrested: PM Ardern
Yama Nabi said his father Haji Daoud, who came to New Zealand from Afghanistan in 1977, was killed at the Al Noor mosque. The attacks killed 49 people and injured 42 others, of those injured, several remain in critical condition.
Democrats upset over Omar seeking primary challenger
Politico reported that Belen Sisa made the comment as part of a discussion in a Facebook thread in which she said that she supports Rep.
Asked his view of the Brexit mess, Varadkar took a contrary view. "I regret that Brexit's happening and the United Kingdom was a really important part of the European Union". "He does great work at Northwestern Memorial Hospital in Chicago", the vice president said to applause.
Mr Varadkar is Ireland's first openly gay leader and one of very few openly gay national leaders in the world.
Theresa May has previously revealed that Mr Trump told her to "sue the EU" and "not go into negotiations".
"I don't think it's something that's imminent but the president was very interested to know how it would work and what the benefits might be".
"I look forward to talking to you later about Brexit, giving you our perspective on it and the real importance of protecting the Good Friday Agreement and the really hard-won peace in Northern Ireland", Varadkar told Trump, referring to the 1998 British-Irish peace accord.
Mr Pence made the comments at a breakfast meeting with Mr Varadkar and his partner at the vice-president's residence in the capital.
At the traditional shamrock presentation at the White House on Thursday evening, Mr Varadkar praised Mr Trump's ambitions to "make America Great Again".