After months of speculation - and public denials - that he would soon be making a switch from Assembly to federal politics, Seselja picked up the phone to Humphries late on Sunday afternoon and suggested the pair meet face-to face for a chat.

Humphries knew what was coming.

Momentum had been building in recent days.

Seselja couldn't bear another term of opposition in the Assembly; he knew he couldn't win the lower house seat of Canberra from Labor and even if he did, he wouldn't keep it for long.

He had crunched the numbers and was convinced he had them, if he wanted to make a move on one of his own side for the Senate.

During a short and curt meeting inside Canberra's Mawson Club on Sunday evening, Seselja told Humphries he was nominating for the Liberal's number 1 spot on the ACT Senate ticket.

It's usually a comfortable win for the Libs and Humphries has not had to fend off any preselection challengers since first winning the seat in 2003.

Careful not to give too much away to other patrons inside the Mawson Club, the pair kept their poker faces while one told the other what he didn't want to hear.

It was just the two contenders leaning in to each other.

After 10 minutes, Seselja had let Humphries know he was coming after him, Humphries made it clear he wasn't going to roll over, and the two parted company.

Seselja's sense of entitlement and his team's lack of discipline played out during Monday's news conference to announce the decision.

Asked if he felt intimated by Greens' Senate candidate Simon Sheikh, Seselja was left embarrassed as his staffers in the room burst into loud laughter and called out ''no''.

Listening to it all on the radio back in his Civic office, Humphries wasn't laughing at all.