But voters know little about Cunliffe. They may have watched his brazen undermining of Shearer's leadership at Labour's annual conference in 2012. They may have heard his disingenuous-sounding denials that he was fomenting trouble.
While Cunliffe has a keen sense of humour, he is seen as someone people have difficulty warming to. National believes that when it comes to trust, Cunliffe still has much work to do.
John Key set the ball rolling this week by labelling his Labour counterpart as someone who was very "tricky". That was a softer word than "untrustworthy". Deliberately so. Getting personal can easily backfire. National's modus operandi is to prod voters to draw the right conclusion themselves.
In that respect, the past week has been one step forward and two back for Cunliffe. It has been his most harrowing week since he became leader five months ago.
The "tricky" verdict would deservedly be thrown out of court if Labour's Best Start package, unveiled last Monday, proves as popular as Labour MPs are claiming it is.
But until the polls show that to be the case, Cunliffe is going to have to invest time in bridging what might be called the "trust deficit".
Best Start is most notable for its promise of a $60-a-week payment to families with newborn babies. The policy is Labour's strongest pitch yet that when it comes to tackling child poverty, it is far more committed than other political parties.
The near-universal nature of the payment - recommended by no less a body than the Commissioner for Children's expert advisory group on child poverty - has enabled Labour to offer financial relief to a broad swathe of middle-income voters without looking self-serving in doing so.
Something was missing, however, from the explanatory paperwork handed out to journalists covering the policy's launch in west Auckland.
The material made no mention of the policy's stipulation that those qualifying for the $60-a-week "baby bonus" would not get any money until their household's eligibility for paid parental leave had been exhausted.
As Labour intends to expand paid parental leave from the current 14 weeks to 26 weeks, Cunliffe's assertion in his speech notes that "all" families eligible for Best Start would get the weekly $60 payment "for the first year of their child's life" did not tell the whole story.
Cunliffe subsequently blamed a speech-writer for the wording. And - to be fair - the policy and the conditions governing the varying amounts of cash to be paid to families during the up to three years that their child might qualify for assistance were mostly spelled out in detail on Labour's website.
Mostly. There was scant mention of Labour's intention to abolish the parental tax credit to help fund the new policy.
That tax credit is worth up to $150 a week for some families, and covers the first eight weeks of a baby's life. That is equivalent to 20 weeks on Labour's new scheme.
There is further evidence Labour's scheme is not as generous as it might appear at first glance.
The first income-tested payment for 1-year-olds will not occur until April 2017 - more than three years away. Meanwhile, Labour has quietly canned its 2011 policy to pay the $60-a-week in-work tax credit to beneficiaries.
Labour has done itself no favours by failing to be totally upfront about its intentions. Reporters at the policy launch should have been able to rely on the information given to them. They will be asking whether the absence of important facts was a genuine mistake or an accidental omission on Labour's part, or whether they were being deliberately kept in the dark in an attempt to increase the chances of uncritical coverage of the baby bonus.
Buying a fight with the media is not the smartest way to kick off election year.
As it was, coverage of the baby bonus shifted markedly as Key - like a pig in muck - ruthlessly and sarcastically picked up on and picked over Labour's less-than-open stance on paid parental leave and the abolition of the parental tax credit.
National's initial line was to accuse Labour of spending money from the proceeds of the economic recovery before the recovery has taken place.
Key then switched attention to the $150,000 income threshold for payment of the first year of the baby bonus, slamming it as "Labour's definition of poverty".
Labour retaliated by using the week-long debate in Parliament on the Prime Minister's annual statement to paint a bleak picture of a country where the Government was "arrogant, out of touch, and out for its mates".
Labour's rhetoric has noticeably toughened under Cunliffe - and for one reason.
There seems to be no mood in the electorate for a change of government. Without such a mood, Labour - which anyway does not look ready to govern - and the Greens - who do have their act together - have to manufacture one.
The trouble is the rhetoric simply does not wash.
Enter Key. He intends making things even harder for his opponents. Don't be fooled into thinking his advocacy for a change of flag is some innocent diversion.
He is doing it on the back of a rapidly strengthening economy and much healthier levels of national confidence. Arguing for a new flag is an opportunity for him to display leadership and make people feel good about themselves and the country.
It is all about nationhood. It is all about patriotism. It is all about gathering more votes for National.
