None of the above because I'm sure you mean national debt rather than deficit, and the answer is Nixon.
OMB historical table 7.1. FY 1969, gross federal debt.
Which is why I tactfully stopped at 5 Republican Presidents when setting it up.
Eisenhower is the last Republican President to reduce the deficit. I am not sure on debt but I think you are right.
I just noticed someone picked Reagan. Got a good laugh out of that one.