First Minister Peter Robinson has taken a verbal swing at Martin McGuinness as they prepare to fly out to America today on a joint investment trip.
The DUP boss and Deputy First Minister will take part in a series of high-level meetings in Washington before St Patrick's Day.
But last night Mr Robinson said that six months after Mr McGuinness shook hands with the Queen in 2012, Sinn Fein was voting to restrict displays of the Union flag at Belfast City Hall.
And he argued the attitude of Sinn Fein to the on-the-runs controversy and the IRA commemoration in Castlederg showed it was "once again taking a stance of 'Ourselves Alone'".
He aded: "In the last few years Sinn Fein has stepped back from the tentative forward steps that were beginning to emerge. That is disappointing; it's a retrograde step and a failure of leadership."
The attack on his power-sharing partner appeared designed to overshadow the announcement that the DUP intends not to run two candidates in May's European elections.
Mr Robinson told his party's East Londonderry Association's annual dinner: "The reality is that if republicans are going to be politically aggressive, then unionism must be strong."
Instead, the Euro-battle was likely to see no less than six unionist candidates, while nationalism was likely to be represented by only two – Sinn Fein and the SDLP. Unionism was in the same position as the United States in the Cold War, needing "a strong base from which to operate".
Mr Robinson had indicated his party would run a second candidate along with incumbent Diane Dodds if it calculated Ulster Unionists were unlikely to retain veteran Jim Nicholson's seat – a threat TUV leader Jim Allister dismissed as "bluff and bluster".
But last night Mr Robinson again raised the spectre of republican electoral domination: "While nationalists are uniting behind just two parties, unionists are dividing across a wide range.
"That will inevitably make it easier for Sinn Fein to become the largest party at these elections but importantly will make it more difficult to ensure a second unionist is elected to represent Northern Ireland in the European Parliament."
Rounding on his likely unionist opponents, the First Minister added: "UKIP are a national party that wants to see the UK out of Europe – although anti-Euro skepticism is already well provided for in Northern Ireland.
"The TUV want to bring down Stormont and hand power back to those who would sell us out in an instant; NI21 want anything the other unionist parties don't and don't want anything the other unionist parties do...
"The PUP are the political voice of the UVF, the Conservative Party is a national party, with no significant base in Northern Ireland, that wants to see a referendum on Europe, and the UUP is yesterday's party and is presently struggling to find a reason to exist.
"The competition for unionist votes will be intense and each candidate standing – however few votes they may win – will take votes off the other unionist candidates."
STORY SO FAR
Relations between the first ministers are thought to have soured after a deal on flags, parades and the past in the Haass talks collapsed. The DUP boss called the Sinn Fein figure a "dictator". When Mr McGuinness said an assessment if Haass can be rescued would have to be taken near St Patrick's Day, Mr Robinson said leaders' talks would continue for as long as it took.