Republican Presidential candidate Donald Trump speaks at the 2015 FreedomFest in Las Vegas, Nevada July 11, 2015. REUTERS/L.E. Baskow

This is an op-ed by Roger Stone, a veteran of eight national Republican presidential campaigns. His book "The Clintons' War on Women" will be released October 6. He splits his time between New York City and Miami.

Presidential campaigns are always won with big-picture ideas articulated with simple, memorable, and disciplined messaging. Even in a primary, voters respond more favorably to a candidate with a grand vision of what our country should be than to policy wonks. Just ask President Gingrich.

Although I resigned from his campaign effort last week, I remain convinced that Donald Trump — and Donald Trump alone — has the stature, experience, and guts to take on the entrenched special interests and save America from further decline under the failed policies of the Bush-Clinton combine. I have wanted Trump to run for president since 1988.

Donald Trump soared in the polls this summer by delivering exactly that kind of message: Make America great again. He wants to fix the immigration problem, create a job boom, make our enemies respect us, end the one-sided trade deals, and take care of our veterans.

In a political climate dominated by special interests, Trump is a breath of fresh air. He's widely known as a savvy businessman with enough of his own money to ignore the lobbyists and donors seeking influence. Trump isn't beholden to the Super PAC-funding billionaires. He is a billionaire. Rather than fall for the left's divisive class politics, voters got behind Trump immediately. They know only a successful business leader can bring jobs back to the US instead of China. He was the only candidate with the courage to say what they were thinking, and they loved it.

While pundits were wringing their hands over his blunt talk on issues that matter most to the base, voters were praising his honesty at their kitchen tables across America. His "controversial" statements about immigration put the issue back on the table in a meaningful way and struck a chord with voters of many stripes. His warnings about China and Mexico stuck to the same core message.

Trump's early success shouldn't surprise Republicans at all. Ronald Reagan, whom I worked for in three presidential campaigns, rarely got down in the weeds in his speeches and debates, always sticking like glue to his overall big picture of the Shining City on a Hill that our enemies would respect and our allies would trust.

Roger Stone, left, with Ed Rollins, center, and Lee Atwater in 1984 discussing strategy for President Reagan's reelection campaign. Ira Schwarz/AP

Many Republican candidates like to compare themselves to Reagan, but most of them need to read more about him. Trump’s background and style are different from Reagan's, but his big-picture themes are very similar. Like Reagan, Trump gave voters a clear, simple vision of a great America and pointed out that the stakes are too great to worry about offending those who would make America weaker. Both have used the kind of direct language that makes our enemies and economic competitors nervous.

What Trump's campaign is suddenly missing is Reagan's message discipline. Trump must not let his campaign degenerate into a series of personal feuds that will only divide the voters he needs to unite in order to win the nomination and the election.

Trump is at his unscripted best when speaks bluntly about America, not about himself. His squabbles with reporters like Megyn Kelly are not what most voters want to hear. He's not running against Megyn Kelly, but against 15 professional politicians and a brain surgeon. The base wants to hear what Trump plans to do to beat China and Iran, not Fox News.

Roger Stone. Business Insider

Trump can correct his course while he's still leading the polls, but he needs to do it fast. His messaging has to get back to what made him the front-runner in the first place and keep his arguments with journalists out of sight, where they belong.

He must establish and maintain his consistent uplifting core message to withstand the tsunami of multimillion-dollar attack campaigns on its way from his opponents. And if his campaign doesn't make sure he's on the ballot in all 50 states, he might as well pack it in. Voters have proved they are ready for a gutsy, independent candidate to speak for them and get America winning again.

It can only be Trump, but only if he shuns the yes-men and gets back to his core message. The stakes are indeed too great.