:::::There's lots of reasons for that shift. The Labour Party choosing to step aside, the Somme, a changed international mood (e.g. Versaille and the Fourteen Points), IPP support for partition, etc. The conscription crisis really cannot be forgotten about. Sinn Féin lost three by-elections in 1918 before the conscription crisis. Brian Feeney has the following to say about Representation of the People Act 1918 in Sinn Féin a Hundred Turbulent Years: 
 :::::"In 1918, as a result of electoral reform, all men over twenty-one and women over thirty had the vote. This provision almost trebled the electorate from 700,000 to just over 1.9 million. ... It was this new electorate that gave Sinn Féin its massive endorsement. It is often overlooked that the IPP's candidates, even in contests in the west and southwest, actually sustained the party's vote quite well. But the old party was simply not attractive to the new young voters, mainly women, and was swamped by them ... 
 :::::December 1918 was the real test of the IPP after decade of incredible change. Twenty-five constituencies may have been granted to Sinn Féin unopposed, but the 1918 election was also the first time since 1910 that 63 constituencies had been contested at all. Also, remember that Sinn Féin didn't officially shift from monarchism to republicanism until 1917. In the mean time there was the formation of the UVF, the Curragh Incident, etc. 1916 was one of a maelstrom of things that happened 10 years that has today's decade being (rightly) called a decade of centenaries.