Aridas
Crazy Little Green Dragon
I'm assuming there was no republican challenger, since he is the incumbent. And if there was a challenger, they did not get any delegates. They only acknowledged Sanders because he came in second in the delegate count, IIRC.
There were 4 other Republicans who challenged Trump in the primaries. Or, at least, they did in the states where the GOP allowed Trump to be challenged in the primaries. In a number of states the GOP decided to cancel their primaries or caucuses and simply declare Trump the winner of their delegates. I believe the number of states where Republicans held presidential primaries this year was less than 20.
In addition to many states deciding not to have a Republican presidential primary, the RNC decided there was no need to hold any debates among the candidates, as that would have helped Republican primary voters be aware they had other choices besides Donald Trump they could vote for, so they didn't hold any.
The other candidates for the 2020 Republican presidential nomination were former Massachusetts governor Bill Weld (who received close to 450,000 votes in the primaries he was able to compete in); former Illinois representative Joe Walsh (who received close to 175,000 votes); real estate developer Rocky De La Fuente (who received a little more than 100,000 votes); and former South Carolina governor Mark Sanford (who received a little over 4,000 votes).
While Democratic primaries generally apportion delegates based on what percentage of the vote different candidates receive, for 2020 the national party leaders urged states to go with winner-takes-all for their primaries. I'm not sure which states went that way, but Trump won by large enough majorities in all the states which held GOP presidential primaries to receive all their delegates, and he was awarded all the delegates in the states which didn't hold primaries. That's why none of the other candidates will be placed into nomination or receive any votes at the convention. But there were indeed other Republican candidates, even though relatively few people seem to be aware of that fact.
Technically, Bill Weld apparently did win 1 delegate. He dropped out after Trump had enough to win, though.