finished now but some explanation needed
17a poor president like this incumbent
p?n?i?e?s PENNILESS. Can only see relevance t poor.
55a touring island, doctor practised a branch of medicine
p?e?i?t?i?s PAEDIATRICS. Where is island ?
The definition is "poor" and the answer is "penniless". President "like this" (ie penniless, or missing the p) leaves the word resident. Resident can mean incumbent.
That's the way I see it anyway. Hope it makes sense.