(1) He doesn't; (2) No.
This case is a non-starter.
The guy would have standing to sue as a member of the Democrat Party and as a Voting Citizen of the United States. As a Democrat he would be compromised by his party nominating an ineligible nominee. As a US Citizen his rights would be compromised by an ineligible nomination by disenfranchising his vote.
There is certainly standing. If there was no standing the TRO would have been dismissed on that basis. The Judge makes a determination of standing before issuing any ruling. He denied the TRO but held open the Motion for Injunction until the other Parties have been served.
I wouldn’t dismiss this suit so fast. My guess is that the Republicans have been waiting to hit him with this after the nomination anyway.