The war will certainly cost more than the $60b and change that the President is asking for. But it is not going to run us several trillion dollars (though even if it did, that would work out to less than 0.1% of GDP over the next 20 years.)
When McMegan wrote the article, GDP was 10 trillion. So 2 trillion would come to 1% of 20 years of that, not 0.1%. This would be more excusable if she hadn’t spent half the piece whining about how 2 trillion was 20 percent of GDP.