There is absolutely no double-spending threat, bitcoin is an ultimate solution to this problem. let's elaborate more:


What is the double-spending problem?
For s digital token to be used as peer-to-peer electronic cash, a medium of exchange, it is absolutely necessary to have an inflation regulatory mechanism because digital streams are reproducible trivially bu consuming almost zero resources. Owners of digital assets have full incentives and sole power to send multiple copies to different users. Electronic signatures are of negligible relevance to help with mitigating this issue and trusted third parties gain too much power. A decentralized, trustless, permissionless, open solution is the only acceptable solution to this problem.

How bitcoin solves the double-spending problem?
The most critical game-changing innovation of Satoshi and bitcoin is the core idea of using a distributed ledger, synchronized by consensus. PoW and game theory are used in bitcoin as instruments to prevent spamming and adversary behavior by establishing a fair voting mechanism. As long as the distributed ledger is balanced and there is no inflation we have the solution and whether the instruments used are perfect or not is irrelevant. They are secondary problems.


Is bitcoin perfect?
Hell no! Bitcoin is just a first attempt to implement the solution, besides there is no such system in the universe, a perfect system! The most important flaw is bitcoin, which I've been investigating/trying_to_address for a long time is the infamous pooling pressure flaw and its 51% consequential threats.


Is the 51% problem a cloned form of the double-spending problem?
No! The 51% problem is secondary and has nothing to do with double-spending because it has no irregular inflation consequence. The main concerns with 51% are fraud and censorship/DoS vulnerabilities.

Is there any built-in countermeasure to mitigate 51% problem?
Yes, there is, PoW plus game theory, the former is flawed (pooling pressure)but working now and the later is not flawed.  

Is the "rational behavior assumption" in the way game theory is employed in bitcoin is a flaw?
No, it is not. There is no version of game theory without such assumption and it has been used in economics and politics exactly the same way as bitcoin is using it.

What's the point?
The point is about the infamous "Don't trust, verify" and how it is exaggerating the situation with miners in bitcoin. Putting trust in miners is discouraged too much and in a vague and confusing way. It is a major obstacle in the development scene of bitcoin IMO.