The DUP smoothed Mr Johnson’s path to Downing Street by outright rejecting former PM Theresa May’s Brexit deal.
Critics have said she frittered away unprecedented levels of goodwill and made grave strategic errors over Brexit.
Deirdre Heenan, a social policy professor at Ulster University, tweeted: “Her intransigence, petulance, arrogance, lack of generosity and political myopia have been catastrophic for unionism.”
The DUP’s Free Presbyterian religious base was also upset with Ms Foster last week after she and two of her ministers chose to abstain on an assembly vote to ban gay conversion therapy.
