Donald Trump in Albuquerque on May 24. (Brennan Linsley/Associated Press)

Fred V. Malek is co-chairman of Thayer Lodging Group and finance chairman of the Republican Governors Association.

Republicans across the country were stunned last week when Donald Trump lashed out at Gov. Susana Martinez during a campaign stop in her home state of New Mexico, and rightly so.

As the party of Lincoln, Republicans have two governors of Hispanic descent and three highly respected female governors. Trump needs to court and gain the support of leaders like these, who represent the strength, competence and diversity of the GOP — not attack them. Many Republicans, including myself, are coming around to support him, but we also believe it is imperative for Trump to recognize that the time for slash and burn is over.

This approach worked to attract 5  percent of eligible voters, but it won’t work to unify the electorate in November. During the primary season, one-third of eligible GOP voters turned out, and not much more than one-third of those voted for Trump. He does not have a mandate.

Trump left a post-primary trail of broken bones and shattered glass that does not heal quickly or easily. He demolished his opponents in belittling and often vulgar terms. Look at it from a personal perspective — if someone repeatedly hit one of your sons, often below the belt, wouldn’t you need some courting and cajoling to consider making up? It’s Trump’s job as the GOP’s leader to unify, to bring people together, not divide them. People want to be with him, but there is still a lot of persuading to do.

At a rally in Anaheim, Calif., on May 25, Republican presidential candidate Donald Trump said he has "a sore that's worth more money than" Mitt Romney. He also said the 2012 Republican candidate was "stupid," a "choker," and that he walks like a penguin. (Gillian Brockell/The Washington Post)

He has made a good start by meeting with House Speaker Paul D. Ryan (Wis.) and others, including Henry Kissinger and Sen. Bob Corker (Tenn.). These are serious people in the Republican Party, and it will be critical to have more support from leaders like these to rely on for advice, and to build a network that can win a general election.

Republicans are united in their desire to see a stronger economy through less regulation and more private-sector incentives; to reverse the United States’ lead-from-behind foreign policy; to challenge the nonsensical political correctness that has invaded our lives; and to ensure we have future Supreme Court justices who support the Constitution.

Trump has started to lay out his plan to restore the United States to more robust economic growth and job creation. And while his instincts trend more toward pragmatism than ideology, his list of potential Supreme Court nominees is sufficiently conservative to give comfort to the center-right majority in our country.

To Trump’s credit, he recognized that the electorate is changing, and it’s clear that much of the voting population is dancing to a very different tune than many in Washington are used to. The concerns of voters — many of whom are angry — have to be taken into account.

However, what worries many Republicans is that Trump could squander the opportunity to build upon this enthusiasm and the changing electorate if he continues to exhibit such a profound lack of discipline. The leader of the free world cannot lead by instinct alone, nor can a nominee win an election in that manner.

People who know Trump understand that he’s an instinct player. He doesn’t prepare a whole lot and goes with a visceral, gut-level approach to his speeches. It’s hard to believe that he thought through or was advised to attack Martinez in New Mexico, or to wave his arms to mock a disabled reporter some months ago.

It will be critical for Trump to begin reaching out to unify the party, and to begin coming around to projecting himself as the confident, presidential figure that voters expect from their commander in chief.

These attacks on fellow Republicans must stop as we move closer to the general election. The team that Trump is assembling, including veteran campaign adviser Paul Manafort, knows this. (Full disclosure: Manafort was my deputy when I directed the 1988 convention for George H.W. Bush and he is a man of wisdom who was a huge factor in erasing our 15-point deficit to Michael Dukakis during the convention).

Winning a presidential election is always an uphill battle, no matter where you start in the polls. The momentum gained and maintained immediately before and after the respective parties’ nominating conventions can determine the fate of the election. My belief is that Trump can give more thought to how he approaches his campaign without losing the spontaneity and irreverence that many voters admire — but ultimately it will be up to him. If Trump expects to be elected, the time to start this new approach is now.