Having had a good night's rest, I'll add a couple of other important differences.
1) Reagan was NOT an isolationist, he was deeply moved by the Holocaust, and he understood NATO was a necessity.
Again - the contrast with Trump couldn't be more stark. Reagan DID understand as he said by his own words that "nobody but us can" lead the charge for world peace, but he also understood he needed allies to hold it all together. This Pat Buchanan section of the GOP - this AT A MINIMUM borderline anti-Semitic, isolationist ("America first"), arrogant approach to foreign policy now is the predominant GOP theme - from Rand Paul to the President. Because of the years I spent in Europe growing up (5 of my first 14 years), I cringe many times when things are said that sound as if they're directly taken from Nazi propaganda - and I'm hesitant to just label someone, but Trump gives off that stench without question. Reagan was really the last Republican President who was generally popular with the Jewish people - and he threw it all away when he went to Bitburg to commemorate the 40th anniversary of the end of WW2. It was another of his tone deaf decisions, but he paid for it big time.
2) I cannot imagine Reagan invading Iraq after we were attacked by the terrorists based in Afghanistan.
I just can't do it. I've long argued the real break of the GOP with reality - so much as one can say anything is a single cause - was W's decision to toss aside 200-plus years of American precedent and commit trillions to a useless war in Iraq. Remember - the reason the covert war was going on in Nicaragua was because Reagan wasn't going to commit American troops to a Vietnam-type engagement (for which we can all be grateful), so his underlings were financing contras inside the country rather than sending troops. In his last year, the GOP minority in the Senate was still pushing him to be more involved in the old "we have to stop the spread of Communism in Central America," but he wisely knew that little actions become big wars. Again, he wasn't a foreign policy genius by any stretch, but he DID understand that a leader can be overtaken by events in foreign countries as happened to both Truman and LBJ. Hell, it was controversial enough when he send troops into Grenada - but his fear was that the medical students might be taken hostage a la Iran - and unlike Iran, they were out on an island so good luck.
3) Can you even imagine Trump sitting down in negotiations with someone like Mikhail Gorbachev?
It's been kind of rewritten and forgotten now but Reagan's aides were absolutely terrified of his first meeting with Gorby. His tendency to be lazy and take it easy and not read briefing books was well known - so his advisers had MOVIES made about the USSR and their leadership because he wouldn't read a book, but he most certainly would watch films (for obvious reasons). When he met Gorby in Geneva in 1985, he was probably better prepare for that summit meeting than for any other meeting in his entire eight years.
@81usaf92 - not sure if you know about this but in October 1986, those two met in Rejkavik (Iceland) and got into it over the Strategic Defense Initiative (aka the missile defense program). Gorby wanted to focus on that one issue and to stop American research into missile defense; Reagan told him that wasn't even on the table. Back and forth they went over an entire weekend - until the moment when Reagan stood up and said the meeting was over. George Schultz (secretary of State) came out to brief the whole world, and the look on his face was "we came this close and nothing." But when Reagan got back to the USA, he got on TV and gave one of his smooth speeches about "everything was negotiable except two things, our freedom and our future."
Reagan was a union negotiator with an impeccable sense of timing, a guy who played the long game.
If Trump would have been in negotiations with Gorby, we'd all be speaking Russian now. He would have handed over all the research data to SDI - probably live on the networks - and then after signing the worst deal in history, he'd have gotten on TV and boasted about how he was the first President to ever get an arms control deal with the USSR and - oh yeah - "the Russian people really love me." Reagan knew it was better to be feared than loved by the Soviet Union.
4) Reagan's Court appointments
Reagan was the first US President with a big-state background since his old hero, FDR. He used the knowledge he'd gained to understand that the courts were part of his long-term success. His AG (his personal attorney, William French Smith) set up a group called OLP that had as its design an interview process to elicit a judge's general philosophy. Important point: there were no "litmus test" questions asked of the potential nominees. In general, though, they got at least center right judges and occasionally some hard right judges who (get this) were actually qualified to sit on the bench.
Remember this - Reagan was a pro-life President (at least in the song he was singing), but he never sought to make sure he appointed judges that would overturn Roe v Wade. His first appointment to the High Court was Sandra O'Connor, whom he met and liked and thought was a smart lady. (There's another one for you - Reagan was drawn to strong women including his second wife, Nancy, and Margaret Thatcher as well as Jeane Kirkpatrick; the comparison with Trump goes unsaid). When Jerry Falwell brought up that as a state senator from Arizona she'd authorized the informing of pregnant women all of their options INCLUDING legal abortion, Reagan asked her about it. She simply told him that she thought abortion was abhorrent, but her personal views weren't how she was going to judge cases - which unlike the modern dogmatists was good enough for him.
Consider this - back when Republicans considered the ABA an authority, Reagan appointed more judges in the top two categories ("exceptionally well qualified" and "well qualified") than any other President in history. Everyone remembers "but Bork didn't make it," but that was also a very public exception.
Reagan appointed qualified judges to advance his general philosophy of life and justice;
Trump appoints judges based on the notion that they're going to do something for him personally.
Reagan insisted on the independence of the office of the Attorney General, even when his first one was his own lawyer; Trump insists that his Attorney General has an obligation to defend anything Trump does.
Reagan did not have Trump's advantages or upbringing.
He also didn't have his mouth or shoddy track record in business.
Reagan understood we are a country of immigrants.
Trump thinks "only white men need apply" in his actions.
And can you even imagine Trump trying to give the speech after the explosion of the Challenger - on the day the State of the Union was scheduled to occur?
Reagan - we all know the speech, it is a magnificent ode to empathy and determination
Trump - "Today on a lunch pad in Cape Carnival, six astronauts - you know, I don't consider a woman who did nothing more than teach class and win a lucky drawing to be, you know, on the same page as those who gave their lives to the space program.......today, a tragedy occurred in the skies over Atlanta, when the Challenging Space Shuttle......I always like a good challenge, good fit challenge, a good challenging challenge can make us all better ya know - like we're gonna make American better - but this tragedy did not have to happen. I warned NASA that one day we would have a tragic, horrible accident and they were taking too many chances by sending this WO-man to outer space to orbit Venus. They should have listened to me. They really should have. BUT....let us go forth from this tragedy, and I have appointed an investigation body to be led by Jared Kushner and to fix the blame in this problem so that it never happens again. We celebrate the lives of (mispronounces all 7 names)......who gave they lives so American might be great again. God bless America."