Pro-agreement Ulster Unionists have been rallying around their party leader expressing confidence that Mr Trimble would win tomorrow's leadership contest. Many said they were disappointed at the Rev Martin Smyth's challenge. Last night, the UUP deputy leader, Mr John Taylor indicated he would support Mr Trimble, describing Mr Smyth's challenge as "ill-advised."
The UUP leader himself was in defiant mood at a press conference at Stormont yesterday, challenging Mr Smyth to provide an alternative to his leadership.
"What Martin needs to do is to explain to people clearly what the object is and what policy is being pursued in this. I am confident to leave the decision to the delegates and I hope that this will finally clear the air and that the party then will be able to unite around the democratic decision that the council has taken," Mr Trimble said.
The party's MP for Fermanagh and South Tyrone, Mr Ken Maginnis, said he felt that much of the friction within the UUP was based on jealousy.
Mr Maginnis said he regretted the damage that would inevitably be done to the party. "His [Mr Trimble's] position internally will be weakened, his eye will be taken off the ball and we will have to engage in a reunification of the party after the contest."
Sir Reg Empey, the assembly's former minister of trade and enterprise, described Mr Smyth's challenge as a blunder.
He said it was astonishing that at a time when the republican movement had failed to meet its obligations on decommissioning and had faced international criticism, the UUP should provide an "alternative side-show".
The former culture minister, Mr Michael McGimpsey, said Mr Smyth was "clearly out of sympathy" with UUP party members and voters alike.
"In my view, only David Trimble has the political skills and intellectual stamina to resolve the issues of decommissioning and the implementation of the agreement to Ulster Unionist satisfaction. It is disgraceful that the party leader is distracted from this task by disloyalty from a parliamentary colleague."
The chairman of the UUP's executive committee, Lord Rogan of Lower Iveagh, said he was both astonished and saddened by Mr Smyth's move.
Meanwhile, dissident Ulster Unionists have welcomed the Mr Smyth's challenge, saying the south Belfast MP was a "safe pair of hands" capable of reuniting the party.
Mr Smyth, a former Grand Master of the Orange Order, said it was "time to clear the air" within the Ulster Unionist Party.
The dissident MP, Mr Jeffrey Donaldson, last night indicated his support for Mr Smyth, saying a vote for the South Belfast MP would "send a clear warning" to the British government and to republicans "that unionists have given enough".
The former UUP leader, Lord Molyneaux, last night expressed his full support for Mr Smyth.
"There has to be an end to damaging uncertainty and there is a widespread conviction that Martin Smyth has the necessary experience and determination to halt the drift," he said.
The anti-agreement MP for East Derry, Mr William Ross, said he had long been concerned at Mr Trimble's line and would support Mr Smyth tomorrow.
"Quite frankly, when I heard what David Trimble had said in Washington, I believed that the time had come to make our position clear," he added.
A majority of UUP MPs will be backing Mr Smyth, according to Mr William Thompson, the MP for West Tyrone.
Asked whether Mr Smyth could seriously damage Mr Trimble and his policies, even if he were defeated, Mr Thompson replied: "Yes, he can and I hope he will."
"I think it would be difficult to damage the party any further than it has already been damaged. We do not know where our bottom line is. Even Mr Trimble's own supporters did not know what his comments in Washington were about. He acts on his own accord and expects us to follow," Mr Thompson added.
The Ulster Young Unionist Council endorsed Mr Smyth's challenge, saying it sensed hostility towards the leadership within grassroots supporters.
The Queen's University Unionist Association also announced it would be casting its five votes for Mr Smyth.
The DUP yesterday claimed that Mr Trimble was "paying the price for appeasing republicans". Mr Ian Paisley jnr said the UUP was in a "total mess".
"No wonder there are problems within unionism if one of the main parties is in such a complete and total mess. It is not just a mess of leadership, it's a mess over policy, it's a mess over direction."