It takes some tricky math to get where military spending is only 12% of federal spending.

First, a soldier wounded in Afghanistan and being treated in a VA hospital would have to have that cost excluded from the budget.

The department of energy dealing with nuclear weapon waste is excluded from that budget.

The office of a foreign US embassy serving as cover for a CIA case officer is excluded from that budget.

Interest on military deficit spending from last year is excluded from that budget.

In fact, add all these things up which don't fall within this theoretical 12% and it comes to hundreds of billions of dollars.

Military spending is $934 billion in the 2021 budget. It's spread out among different agencies and budget categories, so you must add it all together. It includes:

    Defense Department base budget: $636 billion.
    DoD Overseas Contingency Operations: $69 billion.
    Departments that support defense: $228 billion. They include the Department of Veterans Affairs ($93 billion), State Department ($48 billion), Homeland Security ($48 billion), FBI and Cybersecurity ($10 billion), and the National Nuclear Security Administration ($17 billion).

This is 63% of all the discretionary spending in the budget, i.e. the budget outside of mandatory payments such as Social Security.

It's actually over 3% of GDP.

NATO is an organization of countries near the Russian border. The US could easily get by with 2% or less to defend it's own borders. If Russia invades Germany we can ship and airlift troops and meet them in France (given that Germany won't spend enough to defend itself).