What safeguards did the founders put in place to guard against the excesses of majority rule?

They put the electoral college in place.

Because of the electoral college with the option of faithless electors, the states could not just win with a majority of votes at the expense of minorities. The electors were originally described as people who were supposed to judge the situation for themselves and vote individually, but the winner takes it all system ruined this idea.

In my honest opinion , i’d say franklin d roosevelt was a president that impacted our nation , i say this because fdr is voted among top three best us presidents and he was the longest serving president by 3 terms , usually presidents only supposed to have two terms increments of 4 years , equivalent to 8 years total before election time. and he established the fdic , through the 1933 banking act and he established the us , social security system , during his presidency, and established a national minimum wage , through the fair labor standards act , fdr led the allied coalition to victory in wwii and he played a major role in the creation of the united nations.