The increase in Planned Parenthood funding is due to Medicaid reimbursement for health services.

Just because it’s a federal grant or fund, doesn’t mean the President has control over it.  Maybe he does, maybe he doesn’t.  To automatically infer that Trump is responsible shows a woeful lack of understanding of how complex the Fed bureaucracy is.  Trump is not a king.

I have a friend who did something similar. He has withheld tax for about 30 years. He paid his tax money into a trust account held by a bishop with the undertaking that the money will be made available when our government ceases funding abortions. He won his case back in last century. He is disadvantaged however in that he cannot claim any govt. assistance, medical treatments, pensions etc. and struggles to survive, unable to possess a home or a bank account. He could be, with his skills and knowledge, a very wealthy man, but would rather his conscience be clear.

Nope, it's part of the government's annual budget.  Trump has to veto it.  One can be guilty of murder either by commission or by omission.  In the very least, it's murder by omission.  If Trump were to veto it and then it gets overriden, then it's not on him.  Otherwise, it is.  "I will not sign this budget until funding for PP is removed."  He could also use Executive Orders to attempt to cut it off.

It's objectively a grave sin to vote for Trump under these circuмstances.

I am wondering if double effect can ever permit an evil when there is no necessity to act?

The classic example of double effect is five people are tied to one train track, and one person is tied to another train track.  Trains approach the captives on each track.  You are obliged to render assistance, but there is only time to untie those on one track or the other.

You choose to free the five, even though it will mean the death of the one.

You do not intend the evil effect to the one, and the good effect is 5x the evil effect (ie., satisfies the proportionality requirement).

But in this instance, acting was morally necessary and obligatory (ie., one would commit a grave sin to abstain from rendering assistance).

Voting, when there is no Catholic and/or moral candidate, is not obligatory (ie., there is no moral compulsion to act).

Therefore, does double effect even apply (ie., in the absence of necessity to act)?