SDLP leader Colum Eastwood was downbeat as the results from the local election rolled in from count centres.
"I think it's going to be a difficult day for us," he said, looking at losses in Belfast, Armagh Banbridge and Craigavon, Mid Ulster and elsewhere.
"A lot of people within nationalism are very angry, very fed up (and) wanting to send a message to the DUP to get back to work," he told UTV.
"I think a lot people felt the best way to do that was to vote Sinn Féin and I think this was always going to happen. They will have a very big vote across the north."
In one example of how the SDLP suffered was in Lurgan DEA on Armagh, Banbridge and Craigavon Council.
Councillor Ciaran Toman, co-opted on to the body after colleague Joe Nelson stepped down in 2020, polled fewer than 1,000 firmly at the bottom of first preference.
In the 2019 election, the party fielded two candidates, Nelson and Toman, who managed to garner more than 2,000 votes. In this election, two Sinn Fein candidates were elected on the first count, two more might also win seats.
Eastwood said the party held its own in Derry and Strabane while there were a couple of actual bright spots in Belfast for the party.
Councillor Donal Lyons was quickly re-elected in Balmoral while Séamas de Faoite increased his vote tally considerably, almost doubling the vote he managed in Lisnasharragh in south Belfast in 2019.
And there is also a possibility its candidate in Black Mountain in west Belfast may be elected, stopping Sinn Féin from a clean sweep of six seats as People for Profit's Matt Collins, poll topper in 2019, stumbled.
Paul Doherty managed to secure a very creditable nearly 1,700 votes, more than double his tally last time around.
The Ulster Unionist Party believes there were also some bright spots for the party in this election, most notably winning seats in Derry and Strabane and in the Antrim council areas.
But there was disappointment with the performance of the party in Belfast and Mid-Ulster. They look like losing seats also in Armagh Banbridge and Craigavon.
UUP leader Doug Beattie, like other party leaders, noted the performance of Sinn Féin, which he said was something unionism must address.
"Unionism is likely to take a hit across the board in some shape or form while Sinn Féin grow," Mr Beattie said.
"It's a question for us and what is going wrong, what are we doing? Is it negative messaging, is it pessimism ? - I don't know, but we're going to have to address this."
Mr Beattie also argued that turn out was an issue for unionists.
He said: "The other thing we need to do is get those who are pro-union out to vote and if we can get them out to vote, we have to have to get them to vote for a pro-union political party."
