He is never short of the witty riposte to what are usually good-natured taunts from the Opposition. It is the measure of his humility that, more often than not, he reciprocates with a joke at his own expense.
Not this week, however. Someone or something got to him this week. Mr Brownlee was suddenly transformed into the very kind of minister whose demeanour destroys third-term governments like John Key's.
Mr Brownlee abruptly terminated an exchange with journalists outside National's caucus room on Tuesday morning, sarcastically observing that a reporter's supposed source was bound to know more about readying military personnel for deployment to Iraq than he would as Minister of Defence.
He made a similar quip to New Zealand First's Ron Mark, saying the MP's sources in the Defence Force were getting a bit long in the tooth to still be reliable.
Yet Mr Brownlee ended up more or less confirming what Mr Mark was claiming - that personnel at the Linton and Waiouru army camps were already preparing for deployment as a contingency should the Cabinet give the big tick to sending a unit of military trainers to ready Iraqi troops for combat against Islamic State (Isis).
The real surprise would have been those trainers not doing advance preparation in anticipation of the Cabinet decision.
Moreover, no decision can be made until an advance planning team returns to New Zealand with logistical detail such as exactly where the training unit will be located.
The puzzle is why Mr Brownlee did not simply declare all this upfront. It was hardly a state secret. He would have saved himself a lot of bother.
When he picked up the defence portfolio in Mr Key's post-election reshuffle, Mr Brownlee could have been excused thinking his new responsibility would be a comparative doddle when lined up against his other principal role of Earthquake Recovery Minister.
His new role could end up being just as nightmarish and even more thankless. Mr Brownlee's state of mind may well reflect increasing angst within Government ranks about the political risks in such a deployment which will far outweigh any impact on the fortunes of Isis.
The fact is that there will be precious little upside and an awful lot of potential down side. That was not so obvious a month ago when the Prime Minister set out the options for New Zealand's contribution to Operation Inherent Resolve - the name the Pentagon in Washington gives to the United States-led intervention in Iraq.
Mr Key played things very cautiously, ruling out sending any combat soldiers and making that a bottom-line. He also stipulated training personnel would be operating ''behind the wire''. The closer the Cabinet gets to a decision. the more questionable it seems such a deployment becomes.
The biggest question is why bother. New Zealand's contribution will be token. It always is. But it allows the United States to run another country's flag up the pole, thus adding more legitimacy to the overall operation. Or so the Americans would like to believe.
Labour argues Mr Key consequently is unable to make the case for the deployment. Labour is wiping its hands of the whole business, thereby leaving National without the valuable cushion of bipartisan support should some of those deployed end up coming home in body bags.
Labour judges there is already precious little public enthusiasm for this foreign adventure. But there is another reason why Labour is not keen.
A ghost is stalking Wellington's corridors of power. It is the ghost of Anzus - the now forgotten post-World War 2 defence pact which obliged Australia, New Zealand and the United States to come to one another's assistance if under attack.
It is not a welcome apparition. Anzus is a dirty word in New Zealand domestic politics. It signifies the era when Wellington kowtowed to Washington, London and Canberra without question or hesitation.
It was an era which did not really end until the mid-1980s and Labour's promulgation of its anti-nuclear policy. That saw New Zealand briefly treated as something of a pariah in those overseas capitals. The by-product was a more independent foreign policy - or at least the perception of independence. The Labour Party wants to believe that is still the case even if no-one else does.
One of the few advantages of Opposition is that there are no ugly compromises to be made which dilute that independence.
It is a very different story in Government - especially when Uncle Sam comes knocking. New Zealand always complies. That is the deal.
Even former prime minister Helen Clark was forced to succumb to the pressure from Washington and sent two teams of military engineers to Iraq in the wake of the Anglo-American invasion which ousted Saddam Hussein.
For its part, National cannot ignore the legacy of the anti-nuclear policy. That was evident in Mr Key's delayed and ultimately limited offering to the Americans when compared with the bounty offered by Tony Abbott, his transtasman counterpart - fighter bombers and 200 elite SAS soldiers.
Messrs Key and Abbott have floated the possibility of an ''Anzac-badge'' joint Australian and New Zealand training unit being sent to Iraq to participate in Operation Inherent Resolve. It would seem the good old days of Anzus are back again - at least on the right.
In ruling out a combat role for New Zealand troops, Mr Key was clearly hoping to have Labour aboard. But Labour's new leadership has already tested the patience of the wider party by agreeing to vote in favour of amended anti-terrorism legislation currently before Parliament.
National's training mission may have been so designed to make it easier for other political parties to stomach. But there was just too much for Labour to swallow first.
• John Armstrong is The New Zealand Herald political correspondent
