Most of all, a clear message tells voters what a candidate believes and where he or she wants to take the country.
Ronald Reagan was the master of the message. Campaigning on a few key points, he told America how he was going to rejuvenate the economy and defeat Soviet communism. He didn't spend much time on detail. But over and over he repeated his strategic message. It worked.
The two biggest events this past week were Donald Trump's landslide in New Hampshire and Janet Yellen's testimonies before Congress. Trump's message succeeded. Yellen's failed.
An unlikely pair, to be sure. But let's give a quick thought to why Trump got it and Yellen did not.
First up, Janet Yellen. Six weeks ago the Fed raised its target interest rate, with a lot of hawkish talk about three years of sequential rate hikes. Markets crashed in response. And now the Fed is in full retreat.
This is not a clear message. This is not leadership.
Before the House this week, Yellen acknowledged that the Fed's forecast and polices may not be working. (What an understatement.) She pointed to stock market declines and higher credit-risk interest rates. And when asked whether the Fed was changing its upbeat economic view that would lead to more rate hikes, she replied, "Maybe, but the jury is out."
Oil prices and inflation are falling. So are profits. No clear message.
The next day before the Senate, not only did Yellen back off additional Fed rate hikes, she raised the issue of pushing short-term interest rates into negative territory. Whoa. The flip-flop of flip-flops.
That policy hasn't worked in Europe or Japan, and it won't work here. It would destroy savers, again. Banks will go into short- and medium-term Treasuries, which at least have a positive yield, rather than make loans. And negative rates will crush net interest margins for banks.
The Dow fell 231 points following Yellen's stellar performance. Year to date, stocks are off 11 percent. And banks are off 18.5 percent. You're not going to breed economic confidence when the Fed leaves everyone in confusion.
Now let's leave Yellen in the emergency room and move on to a patient who has healed in the message department.
Donald Trump is today mastering the art of the positive. Coming out of an Iowa loss, campaign manager Corey Lewandowski told him bluntly, according to The Wall Street Journal, "We can knock on every door and call every resident. But most important: If we remain positive and focus on our message, we can win New Hampshire."
When I interviewed Trump on the day before the primary, he emphasized his positive message of optimism, growth and national security. In recent weeks, he has talked about how America has been losing key battles around the world, whether it's ISIS, Russia, Iran, China trade, immigration or the declining economy. And he has loudly proclaimed: If you elect me, we will start winning again. Everywhere.
Asked what a President Trump would do about the risk of recession, he reeled off a series of tax cuts, deregulations and federal budget cuts. He knows the country is in revolt against Washington, D.C., and he plays to that with his program.
He talks about oil independence and opening up federal oil fields.
He talks about bombing ISIS oil trucks.
He mentions Anthony Scalia and Clarence Thomas as models for Supreme Court appointments.
He talks about creating jobs -- over and over.
He talks about strong border controls to fix the illegal-immigration problem.
He talks about a strong military and renewed support for our military vets.
He proposes a total repeal of Obamacare, with health savings accounts and creating a more competitive market by letting citizens purchase health-care plans across state lines.
Perhaps most interesting, he is railing against big corporations and their big money deposited in super PACs. Unlike a typical Republican, he hangs out Big Oil, Big Pharma, Big Insurance and Big Lumber as examples of the corrupt monetary influence on American politics.
I asked him if he intended to change the Republican Party. He snapped, "You bet I do. It needs changing."
There are soft spots in Trump's proposals, most particularly on China trade. His tariff threat is worrying Wall Street and pro-growth free-traders such as myself. More work on that will come.
But apart from even these details, Trump's message is clear: America must start winning. And yes, we must make America great again.
Positive and optimistic. Growth. Leadership. Clarity. It worked in New Hampshire.
Janet Yellen, on the other hand, nearly fell off the financial ladder.
Message matters. There's a lesson here for all of us.