During the Treaty debate he asserted that the counties of Ulster which comprised "Northern Ireland" could never be incorporated into an Irish Republic while the British Empire was what it was.

[6] He resigned from Cumann na nGaedheal in 1924 because of dissatisfaction with government attitude to certain army officers and joined the National Party led by Joseph McGrath.

He resigned his Dáil seat on 30 October 1924 along with several other TDs, and the resulting by-election on 11 March 1925 was won by the Cumann na nGaedheal candidate Martin Roddy.

In the 1930s he was involved with the short-lived but widely followed Irish Christian Front, serving as the organisation's secretary and announcing its creation to the public on 22 August 1936.

McCabe chaired their meetings, denied the group was a fifth column and expressed the belief that a German victory would lead to a United Ireland.