President Trump is halfway through his First 100 Days, so it’s time to give him the Ed Koch test. “How am I doin’?” the late New York mayor used to ask, and he always got an answer.

Trump isn’t asking, but he gets a report card anyway. Assessing his start in three key subject areas, I see a mix of solid hits and key misses, with huge potential and reasons for optimism.

On Subject No. 1, whether he is keeping his campaign promises, Trump scores an A. His focus on doing what he said he would do is the best part of his young presidency because faithfulness is the key to restoring Americans’ trust in government.

Corruption in the halls of power is a perennial problem, but more corrosive these days is the near-universal belief that all politicians say one thing and do another. Trump was elected largely because he was an outsider untainted with that baggage, and on that score, he is proving that voters made the right choice.

His focus on fixing immigration, creating jobs and replacing ObamaCare is consistent with his main campaign themes. Two others, tax reform and rebuilding the military, are next in line. Even those who disagree with Trump must concede he is serious about his pledge to put Americans first.

On Subject No. 2, whether he is delivering results, Trump gets a B. From the moment of the election, he eyed low-hanging fruit he could pick through executive orders, which he issued right out of the gate. Those changes already show impressive gains.

Economic confidence is rising among businesses, entrepreneurs and consumers, thanks in part to the president’s push to keep companies from moving plants and jobs to Mexico. He meets regularly with corporate titans, small business owners and unions, all of whom have ideas on getting the economy roaring.

Trump’s order that federal agencies reduce two regulations for each new one is boosting animal spirits, and the stock market surge has added more than $2 trillion to national wealth. To top it off, Friday’s strong jobs report and firm wage growth for February add to the happy sense that growth is accelerating.

Something positive also is happening on immigration, with officials saying the number of people caught trying to enter illegally from Mexico in February was the lowest in five years. Even the New York Times grudgingly concedes the Trump effect, saying interviews in America, Mexico and Central America turned up few people who “quibbled with the idea that President Trump had altered the climate for immigration.”

Simply put, even before the wall is built, America is finally on course to getting border control and creating an immigration system of our choosing.

The contrast with President Obama’s lackluster performance on the economy and immigration is stark. Good ideas and new presidential leadership are bringing swift results that Obama never delivered.

Alas, not everything went as Trump planned. His first order on immigration and refugees had a clumsy rollout and was blocked by the courts, while his second, though more tailored, is drawing suits from states trying to stop it. It is also mystifying that the White House can’t say what, if anything, officials are doing to tighten security vetting in the meantime.

Regarding ObamaCare, the complexity of health care guarantees results will not be immediate, but Trump is not ducking the fight.

With legislation roiling the GOP, he is playing a constructive role by meeting with both sides and encouraging swift resolution while also staying open to changes. His promise to help sell the final measure to the public reflects his commitment.

Subject No. 3, working with others, is the least impressive part of the president’s start and earns him a mediocre C.

His lack of political experience shows in his slow, uneven actions in forming a government. On one hand, his cabinet is generally first-rate, with Secretary of Defense James Mattis, Homeland chief John Kelly and Secretary of State Rex Tillerson looking like stalwart pillars.

Even those who disagree with Trump must concede he is serious about his pledge to put Americans first.

On the other hand, the White House has only itself to blame for being behind schedule in nominating people for the bulk of the 1,100 positions that require Senate confirmation. Combined with the Democrats’ obstruction, the result is too many empty desks and too many Obama holdovers, some of whom are undermining Trump by leaking secrets.

Still other leaks are coming from Trump’s own team. Unflattering reports about him cite sources “close to the president” or “people around him,” which signals inner-circle discontent. That is troubling so early in an administration.

Most worrisome, Trump often seems like a lone ranger fighting the world. Even Superman needed help, and governing is a team sport.

His explosive tweets accusing Obama of wiretapping him caught Trump’s aides off guard, and reportedly resulted in him having furious arguments with Steve Bannon and Reince Priebus.

While Trump is right to suspect he is the victim of dirty tricks started by the last administration, his accusing Obama personally was a combustible way of making the point and probably ended any possibility of a constructive relationship.

Some critics blame Trump’s use of Twitter, but he has no intention of giving it up and I don’t blame him. Twitter gives him a fast way of speaking without the filter of a press corps that is biased and hostile, and conveys a personal touch that official statements don’t.

Yet the advantages disappear when he uses it to pick a fight nobody on his team is ready for. The all-hands-on-deck alarm pulls everybody into an emergency and locks him into an agenda that hasn’t been discussed and may be a mistake.

It also reinforces fears that Trump is too undisciplined. While his free-wheeling style is often refreshing, many Americans still find his unpredictability unnerving.

On other subjects, such as his response to challenges from foreign adversaries, it is too soon to offer a grade.

When I interviewed Trump before the inauguration, he said he didn’t expect to be tested by Iran, Russia, China and North Korea.

“I’m not a game player,” he told me. “They understand me.”

Yet many of those powers are indeed testing the new president to see how he reacts to provocation.

Trump so far has kept his cool while signaling he won’t turn the other cheek. Still, we have no idea how any of this will turn out, so a grade would be premature.

The domestic report card then shows an A, a B and a C, giving the president a solid B average for the first 50 days. That’s a very good start and there is opportunity for big improvement when he gets more experience and has his full team in place.

Here’s the best news: We have a president determined to succeed and willing to work tirelessly to make America great. That’s why I remain optimistic.