You have the right to remain silent about your opponent. Anything you say can and will be held against one of you in the court of public opinion. You have the right to hire consultants who proffer bad strategies. If you cannot afford to take that advice, ignore it. The voters will provide you with their concerns free of charge.
In fact, here's my free advice. The primary voters have largely made up their minds. At this point, we've been subjected to over a year of campaigning. We know how you're different from each other. Those of us who remain undecided just aren't that invested in who wins. Any further criticisms of your Democratic opponent is in effect delivering free oppo to the GOP. From this point forward, the winning strategy is to tell us how you're different from the Republican candidate.
Whoever wins the nomination will be subjected to the same narrative from that side of the fence. You'll be painted as a defeatist who can't accept impending victory that is "just around that corner" in Iraq. Start exploding that myth now. You'll be painted as a socialist who wants to rob the hardworking taxpayer to subsidize health care for lazy poor people. Start selling the need for a national standard system now. You'll be painted as a 'tax and spend' Liberal who wants to deny capitalists their 'hard-earned' gains. Expose the trickery of trickle down economics now. Highlight the Republicans' fiscal irresponsibility. Showcase GOP driven income inequality to justify the need to close tax loopholes, end the tax cuts for one percenters and maintain the estate tax.
These are all complicated issues that will need to be explained to the general electorate in small bites. If you wait until September, you cede the advantage to the GOP, whose heir apparent will frame the memes first. In short, the time is past to tell us why one of you is better than the other. It's now time to start telling us why both of you, either of you, are better than any Republican candidate. That is if the end goal is to put a Democrat in the White House.