While the language may have been slightly different, Ed Miliband sent out a similar message to the Conservative leader yesterday - calling for a public fight over which of them is the stronger leader.
Alongsides the headline- grabbing announcements about freezing gas and energy prices and abolishing the bedroom tax, 'Red Ed' as he was inevitably re-dubbed, tackled head-on the issue that had dogged him ever since he won the Labour leadership - whether or not voters believe he is Prime Minister material.
His case was hampered by an opinion poll, released just an hour before he took to the stage in Brighton, which showed that six in 10 Britons did not view him as an election winner.
Half thought Labour would have a better chance in the next election if someone else was in charge.
If he had read the bad news, Mr Miliband showed no sign of it as he confidently and unhurriedly stepped to face hundreds of Labour delegates and a pack of press photographers.
It was a slightly different Mr Miliband from the one Labour members have seen in recent years, more relaxed and more able to laugh at himself.
Labour strategists were also very brave. A montage of shots showed him in action, meeting ordinary people, touring high streets, all leading up to that most traditional of political cliches - a baby.
Unusually, however, the baby in question was very clearly yawning. It could have seemed a perfect metaphor.
So, too, could Ed's extended riff on his reputation as a "geek". Or the fact that Steve Coogan, aka Alan Partridge, was in the audience.
But with only a few stumbles in more than an hour of speaking with no notes, the Labour leader, for the most part, carried it off.
Gone was the language of maybe, someday... and in its place was certainty. He talked over and over again about what his government would do when it was in power, not if.
And he painted Mr Cameron as weak, unable to stand up for ordinary Britons in the face of big business.
Mr Miliband said he was strong enough to admit his faults, strong enough to suggest he felt nervous on his first day as Labour leader and strong enough to stand up and demand more for voters.
He told the Prime Minister that if he wanted a contest about leadership and character "be my guest".
He also hit out at Mr Cameron's Australian election guru Lynton Crosby, who had been accused in the past of using "dog whistle" politics to appeal to right wingers.
Political observers point out that while Labour's new slogan 'Britain Can Do Better Than This' could appeal to voters looking for a better future, it had one vital flaw - Labour cannot use it on campaign posters alongside pictures of Ed Miliband.
There is nothing to stop the Conservatives from doing so.