The debate, held at Swedish Television half-way between two national elections, was at times heated, in particular when debating the subject of who would be prepared to govern with whom after the next election.
Last week, the leader of the Liberal Party Jan Björklund reignited that discussion when he said he would prefer the four party centre-right Alliance govern together with the Social Democrats rather than seek the support of the anti-immigration Sweden Democrats.
During the debate at Swedish Television, the other party leaders in the Alliance were put under pressure to clarify their positions. When it was the Social Democrat leader Stefan Löfven's time to speak he went on the attack, calling the Sweden Democrats "a Nazi party, a racist party". He added that when the current leader of the party, Jimmie Åkesson, joined the Sweden Democrats "swastikas were still in use at the meetings".
"You are lying! What meetings?" exclaimed Jimmie Åkesson.
In a statement on Sunday, while the debate was still ongoing, the Sweden Democrats vowed to report the prime minister to the constitutional committee. They accused Löfven of belittling the Nazi's crimes against humanity
"When Sweden's prime minister claims that the Sweden Democrats are a Nazi party it is not just a lie, but also completely lacks understanding of history and lacking in respect for all those millions of people who have been exposed to real Nazism," said Jonas Millard, the party's own representative on the constitutional committee.
Referring to the constitution, Millard said that a prime minister's statements must be "correct and fact-based" and that the party would therefore report him to the parliament's Constitutional Committee. It is formed of prepresentatives from all parties. After a hearing it can decide to criticise a member of the government.
After the debate, Stefan Löfven said his words had come out wrong.
"It could be that I said it wrong. But it is a racist party with Nazi roots," Löfven told Dagens Nyheter.
The Sweden Democrat party was formed in the late 1980s, and several of its founders were at the time also active in the extreme right-wing organisations such as the neo-Nazi Nordic National Party and Bevara Sverige Svenskt ("Keep Sweden Swedish"). The Sweden Democrat party today has a distinctly anti-immigration profile, but maintains it has moved on from its past.
Last week, a Sweden Democrat MP commented on a private members bill that she had tabled where she wanted to scrap the current system of press subsidy. Anna Hagwall explained to the news paper Aftonbladet that she wants a regulated media market, and that ethnicity should be a factor to consider when issuing publishing licences.
"No family, ethnic group or company should be allowed to control directly/indirectly more than five per cent of media," she wrote in an email to the paper.
The biggest private media company in Sweden is owned by the Bonnier family, who have long been the target of anti-semitic attacks.
Over the weekend, the Sweden Democrats announced that Anna Hagwall would resign from all political assignments for the party, and that she would not be running as an MP in the next election.