Sinn Féin leader Mary Lou McDonald said she acknowledged Trumps comments on a united Ireland and said the onus is on the Taoiseach to begin planning.
“Our national journey is now reunification, which is organised, planned and a peaceful transition.”
Democratic Unionist Party (DUP) leader Gavin Robinson said Trump “knows better than most that elections matter”.
“Northern Ireland’s constitutional future will be decided by the people of Northern Ireland, not by commentary in London, Dublin or Washington,” he said.
He added that Northern Ireland is part of the UK because it is the “settled democratic will of its people” and added he is confident the country will continue to choose the UK.
Former DUP MP Ian Paisley and close friend of the Trump family said: “everyone is allowed a personal opinion even when it’s wrong”.
Welcoming his comments, the leader of the Social Democratic and Labour Party (SDLP) Claire Hanna said there was something “fairly extraordinary” about Trump standing in Dublin and talking openly about Irish unity.
“When even Donald Trump has clocked that Irish unity is no longer some distant or theoretical prospect, it tells you something about just how far this conversation has shifted.”
The Ulster Unionist Party (UUP) leader Jon Burrows said while America is an “important ally,” Northern Ireland’s future will be decided by its people.
“That is the principle of consent, now enshrined in law through the Belfast Agreement.”
The Traditional Unionist Voice (TUV) leader Jim Allister said Trump “is not the first US President to meddle in the affairs which don’t concern him”.
“Northern Ireland not a pawn in Trump’s fall out with the UK. Our constitutional future does not depend on him or any other foreign dignitary,” Allister added.
Ireland’s Foreign Minister Helen McEntee said: “Something to this magnitude can only happen where there’s consent from the Irish people.
“It’s something that that we have to work on and we have to work towards.”
Later, while attending an event at the US Ambassador to Ireland’s residence, Trump said there is “no good answer” to a question about a united Ireland.
Recalling the moment, he said: “Oh that’s a nice question, I have a nice answer, I think, we’ll read about it tomorrow.”