OTTAWA—Erin O’Toole insists the Conservative caucus is united behind his leadership. But can he be as confident about the party’s grassroots? The reaction from a handful of third-party organizations, which represent swaths of the Conservative faithful, suggests the answer is likely a no. “If they keep throwing their base under the bus, there’s not going to be anyone on the bus,” said Sheldon Clare, president and CEO of the National Firearms Association, adding that he remains a Conservative member for “right now.” Gun owners and their advocates were among those O’Toole courted both times he ran for party leadership, first in 2017 and again last year, when he was successful. Clare says the community reacted with shock, anger and disgust  during the September federal election campaign when O’Toole backtracked on his promise to repeal the Liberals’ ban on some 1,500 types of “assault-style” firearms. Facing attacks from the Liberals, O’Toole …