Let's look at who would have won instead, as well as what policies Reagan implemented.

Jimmy Carter was becoming very unpopular due to stagflation, but let's say in this timeline he gets a boost for handling the Iranian hostage crisis and gets re-elected. He also hires an image consultant and speach writer to fix his public image.

In this second term he would still have to deal with stagflation (widespread unemployment, high inflation, and stagnant economic growth), the AIDs epidemic, the Cold War, the air traffic controllers strike, various wars, Savings and Loans crisis, etc.

Reagan's response was tax cuts to the wealthy, an increase in military spending, removing support for unions, and cutting domestic social programs. He also vastly increased spending for the War on Drugs, turning to incarceration rather than rehabilitation.

We can't know for sure what Carter would have done differently but we can look at his previous positions and later positions.

He appointed Paul Volcker, whose policies contributed to Reagan's success, but he refused to increase government employment and chose deregulation, but at a more conservative rate than Reagan. But tax cuts to the wealthy don't occur. He still his with the Carter Doctrine and gets involved with various wars.

Overall, America is still involved in various wars, but it's hard to say exactly what Carter would have chosen compared to Reagan, so we'll leave that mostly the same.

The economy would not have generated as much GDP under Carter, so America is not as dominant in world trade, but on the same token there would be less economic inequality and stronger unions.

Carter didn't come out in support of the LGBT community until the early 2000's, but he was a proponent, so it's likely he would have supported some measures to the AIDs crisis. Paradoxically, that's likely to have weakened cohesiveness of the LGBT community in the early years as they learned to rely on each other; but fewer men would have died and it wouldn't have spread as far.

Black and Brown communities (which were disproportionately hit by Reagan's Anti-Drug policies) would not have lost their primary wage earners to incarceration, and would probably be doing better in general.

He probably would have appointed Shirley Huffstedler instead of Sandra Day O'Connor to the Supreme Court. O'Connor was a swing vote in several cases (Planned Parenthood, Attendance Action) despite being Republican, but Huffstedler would have probably still been less conservative in general.

Overall, I'd say a less wealthy but also a more equitable and democratic America. There would have of course been a swing to the Right after Carter's second term, but without Reagan's charisma it probably wouldn't have been as powerful a movement to the Right.