Five weeks ago, Donald Trump dispatched his remaining Republican opponents to become the presumptive nominee of the Republican Party. That gave him a predictable bump in the polls and a month’s head start on Hillary Clinton. It also gave him two months to unify the party before the summer convention.

By almost any objective standard, the last five weeks have been a disaster for Trump, in which he’s wasted time and lost support. There are tepid endorsements from Republican leaders who must support the nominee, but many party leaders and funders remain on the sidelines.

Trump already has made a series of rookie errors in a race that won’t allow for many mistakes, including his recent attacks on a judge from Indiana who happens to have Mexican parents. His comments about that judge were called “racist” by Paul Ryan, and the majority of Americans agree.

Trump now has just five weeks left to unify the party before the gavel goes down on the Republican National Convention. If those five weeks are anything like the last five, the prospects of a united campaign in the fall are dimming every day.

In a presidential race, the national convention is a window that allows millions of new voters to take a look at the candidates. Conventions are a springboard into the fall’s election. If they produce a picture that voters don’t like, or when they produce little or no “spring,” the result is often a stupendous belly flop in November.

Without significant changes in the trajectory of Trump’s campaign, this convention will be dominated by media speculation about who isn’t there, who isn’t speaking and why. And by comments from other Republicans about Trump’s fitness for the office.

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The race is a long way from over, but the challenges for Trump will only escalate. He was perfectly suited to running in a crowded primary that never produced a strong anyone-but-Trump alternative. He had name recognition and a larger-than-life persona. And he combined a huckster’s knack for outlandish promises with a magician’s skill at card tricks.

He also got the luck of the draw, running in a crowded field of opponents that turned out to be a mile wide and an inch deep. That allowed him to pile up “winner-take-all” primaries with an average of 38 percent of the vote, which soon enough forced out his remaining opponents.

Trump became the champion of the most frustrated and angry elements of the Republican base, which has at its core older white men who are losing their jobs and their hopes, and are looking for someone to sucker punch.

Now comes the tough part. Here are Trump’s most difficult challenges:

Acting like a president: Trump is still running a primary campaign, attacking Republicans and saying outlandish things. That worked well in the primary, but the scale of a national campaign requires him to pivot quickly to respond to new demands and a more aggressive investigative media. Those Republicans who are waiting for Trump to change and become more “presidential” should prepare themselves for the worst.

A new audience: Running a campaign for the support of mainstream, general election voters is not remotely like running a primary campaign. Simplistic formulas on issues like immigration, national security and the economy produce nodding heads in primaries but can and will be made to look like cartoon answers in general election debates.

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Democratic unity: Trump is the most unifying force Democrats have seen since Watergate. This week, President Obama forcefully endorsed Clinton and will campaign with her on Wednesday. Sanders said that after this weekend’s final contest in Washington D.C., he looks forward to working with Clinton to defeat Trump. Sen. Elizabeth Warren of Massachusetts, a respected leader among progressives, has jumped in as well. The process is accelerating to produce a united convention this summer.

The team: Trump is the opposite of a team builder, which is making it difficult for him to attract and retain seasoned campaign veterans and effective surrogates. Within a few weeks, Trump will be campaigning against a dream team of Democratic heavyweights, including Clinton, Obama, Sanders, Bill Clinton and Warren. Together, they have experience in five presidential elections. Trump’s bench, in contrast, is essentially empty.

The math: The race for president is a state-by-state contest. In this race, the outcome will be decided in these states: Colorado, Florida, Iowa, Michigan, Nevada, New Hampshire, North Carolina, Ohio, Pennsylvania, Virginia and Wisconsin. Obama won all of those states in 2008 and all but one in 2012. Clinton currently leads in at least eight of them.

Trump better get in gear quick or his time will run out.

Alan Caron is the owner of Caron Communications and the author of “Maine’s Next Economy” and “Reinventing Maine Government.” He can be contacted at:

alancaroninmaine@gmail.com