The Department of Statistics is usually a benign presence on the political landscape, but over the past few months it has entered National's nightmares like the grim reaper.
Each month, the relentless tread of Statistics New Zealand's updates on migration echo through Parliament, haunting National with the ghosts of campaigns past.
This year, the innocuously titled "International Travel and Migration" tables have told a tale of ever increasing numbers heading to Australia.
So this week National was again hoping its 2008 campaign billboard - "Wave goodbye to higher taxes, not your loved ones" - had faded from the collective memory.
Without the Memory Charm used by wizards in Harry Potter to make the muggles forget, Bill English has resorted to spinning as ferociously as a spider with a web across the doorway of a Ponsonby cafe.
He predicted Australia's mining boom with its alluring salaries would end and all those New Zealanders would flock home again, with Australian workers heading for the new land of plenty.
In the meantime, English suggested we should celebrate Australia's good fortune for it was also ours.
Prime Minister John Key stepped into the web like a traffic monitor beside a car crash waving rubberneckers on with a "nothing to see here".
In March, Key's defence was that migration levels were high because people were leaving Christchurch for Australia. This month, the exodus was simply business as usual - and no different from previous peaks in migration.
This may be true - since 1980 New Zealand has only had a net migration gain from Australia twice - in 1984 and 1991 - and there have been cyclical peaks and troughs in the levels of net migration loss, usually coinciding with economic downturns.
It soared above 25,000 after the recession in 1980 and 1981, and again in 1988 and 1989 following the stock market crash. There was another peak in the late 1990s after the Asian financial crisis, when it peaked at about 33,000 before dropping back to just over 10,000 in 2003 and 2004. The latest peak came hot on the heels of the global financial crisis in 2008.
However, truth and historical context are hardly a political ally, given Key had previously ignored both to give him that billboard.
In 2008 - during a peak that Key would no doubt now describe as normal - he was calling the level "a vote of no confidence in Helen Clark's Government".
"Record numbers of [voters] are voting with their feet!" he trumpeted.
The net migration loss that prompted that conclusion was 28,000 - just a tad below the 40,000 net migration loss recorded over the past year under National's stewardship.
Key is finding out - as his prime ministerial predecessors found out before him - that the Opposition is an elephant that never forgets.
Labour's finance spokesman David Parker certainly remembers that 2008 billboard very well. With some mirth, he congratulated National on breaking its own record for the third month running. He asked whether Finance Minister English had been holed up in Belarus with shot putter Nadzeya Ostapchuk getting tips on how to improve his performance.
Parker followed that up yesterday by producing a 30-page catalogue of National's failings - including a rather stark graph on the migration to Australia.
Key is, of course, not the first Prime Minister to be hoist on his or her own petard. Had he taken the time to reminisce, he would have remembered a day in September 2008 when he was Opposition leader questioning Helen Clark about her own promises soon after she took office in 2000.
Meanwhile, in Parliament Speaker Lockwood Smith was experiencing another cyclical exodus - that of NZ First leader Winston Peters from his seat in Parliament to the door.
A former television host, Dr Smith is clearly mindful of the ratings of Parliament TV - and the viewer feedback line had run hot the week before with disgruntled members of the public moaning about the behaviour of MPs.
So it didn't take much for him to boot Peters out of Parliament this week for arguing with him. By way of retaliating, Peters had a press conference ostensibly to have a go at Maurice Williamson, but in which his real target appeared to be the Speaker. He claimed that the Speaker was too pedantic and should be shown the door himself.
Unlike those New Zealanders heading to Australia, there was nothing long term about Peters' absence from Parliament. He was back the very next day.
The Speaker could only hope that his own call-up to join the great exodus from New Zealand to take over as the High Commissioner in London would come soon.