With a war raging at the European Union's eastern border, Russia posing a threat, and U.S. President-elect Donald Trump pressuring allies to do more, the bloc urgently needs a viable plan to secure hundreds of billions of euros to bolster its defenses.

But while there is broad agreement Europe should be spending more, all potential options — governments boosting their national budgets, joint EU borrowing or creating a new funding vehicle — come with their own challenges, such as fiscal pressures, political resistance or funding costs.

The bloc estimates €500 billion ($524 billion) of investments are needed in the coming decade, though its new defense chief argues that would only cover an air defense program.