During Reagan's first two years in office, the Democrats really did go after him. But Reagan had the charm for lack of a better word, the connection with the people, charisma perhaps. That by letting all the political attacks roll off his back worked. He would smile, tell a self depreciating jokes, even his enemies would laugh.
One huge difference, Reagan was able to keep independents on his side. Trump has lost their support. Where Reagan kept an average of 52% approval rating among independents during his first two years, Trump averaged 38%. It's with independents that these two depart, one could call it the likability factor. There was little difference among approval ratings from republicans, 82% for Reagan, 83% for Trump. But a huge difference among Democrats where Reagan averaged 31% approval to Trump's 8%.
I think it has/had a lot to do with their personalities. Non-confrontational, soft spoken, but determined vs. brash, confrontational, loud mouth and name caller. Also, Reagan worked closely with Tip O'Neal getting things accomplished, we'll see how Trump and Pelosi get along.
I think if Reagan tried to do what Trump has over the last two years, his personality, style, likability would have accomplished a lot more than Trump has and made a heck of a lot less enemies. Reagan's behavior was presidential whereas Trump's is more out of the WWE than the oval office. Perhaps the biggest difference is that Reagan was able to connect with the people whereas Trump hasn't outside of his base. You're right about the ammunition, Reagan didn't give his opponents any. Trump give his opponents all they need and more by his antics and behavior.