When he started to think that people could believe his model could become true then the campaign was weakened. People hesitated. They started to think if they would have to pay more tax than before.
That can't be the goal of any of the major parties. The people would likely punish them at the ballots for not being able to overcome their inner-party conflicts and finally form a government. They're sick of it.
Even if people agree with the need for reforms, they are uncertain about the flat tax. They are starting to fear that they could be the losers in this reform.