It's not just the carbon tax (though that's the one the CPC is betting on more people understanding and disliking), it's the overall tax risk that Trudeau has created.  

For example, there have been rumours of taxing health benefits, higher capital gains and dividend taxes, and small business tax changes which may have unintended consequences (e.g. Doctor brain drain).  On top of higher payroll taxes and a complete disincentive to succeed and earn over $200k as the government is entitled to more of it than you are.  

None of this tax risk existed under Harper, and many of the current CPC candidates seek to protect families and businesses from this.  

The carbon tax may appear as the wedge issue, but it goes much deeper than that.