To keep the executive in check, the founders decreed that money to pay the executive's army (and every thing else) had to be appropriated by Congress. If Congress didn't like what the executive was doing, it could simple refuse to fund it. Worked in England, back in Cromwell's time.
Doesn't work so well in the modern USA. When Congress cuts off funding, the Democrats wail that they are shutting down the government, the msm takes up the story, and all the takers whoop it up. Today, the Congress doesn't dare cut off funding for anything, lest they be accused of "shutting down the government":.
And the purse looses its power. One more check and balance bites the dust.