Efforts to reconcile Sinn Fein with the senior partner in the Belfast government, the Democratic Unionist Party, have foundered over a number of issues, including a failure to agree on how to deal with unpunished crimes committed during the Troubles.

Image A still from a video posted on Twitter by Barry McElduff with a loaf of Kingsmill bread.

South of the border, Sinn Fein is now the third-largest political party in the Dublin Parliament. It decided in November that it was willing to be a junior partner in a future coalition government there — the latest shift from its original policy of refusing to recognize or sit in any parliament or government other than one representing a united Ireland.

However, the party’s previous links to I.R.A. violence and racketeering are still problematic for some southern voters, who might otherwise be attracted to its center-left social platform and strong constituency work.

Last November, the party’s veteran president, Gerry Adams, who has led Sinn Fein since 1983, announced that he would stand down at the next election, a move interpreted as passing the torch to a new generation of leaders with no personal involvement in what republicans term the “armed struggle.”

Mr. McElduff himself was convicted on charges stemming from his role in the I.R.A.’s false imprisonment of a suspected police informant and was given an 18-month suspended sentence in 1992.

A blurb on the Sinn Fein Bookshop website describes him as an “irrepressible republican raconteur and wit.” In the video on Twitter, since taken down, he jokes: “I’m in the Classic service station here, but I’m just wondering, where does McCullough’s keep the bread?”

The post was immediately condemned by a range of politicians and community leaders. Arlene Foster, the leader of the Democratic Unionist Party, which draws most of its support from Protestants, said in a post on Twitter: “Shame on any elected rep who posted that inhuman video. I feel sorry for IRA victims & West Tyrone who have McElduff as their MP. All murder was wrong. Glorifying any murderer is sickening. Mocking is depraved.”