[Initially] the Supreme Court hammered the New Deal. On May 27, 1935, in a crushing defeat for Roosevelt, it voided the National Industrial Recovery Act and the Frazier-Lemke Farm Bankruptcy Act. It struck down the Agricultural Adjustment Act on January 6, 1936, the Guffey Coal Act on May 18, and the Municipal Bankruptcy Act and a New York state law setting minimum wages for women on May 25.(Helvering v. Davis was the case that legitimized Social Security.)
Enraged, Roosevelt decided to subdue the Court. His megalomania inflated by his 1936 landslide, on February 5, 1937 he abruptly asked Congress to enact a bill empowering him to appoint one additional Justice for every one who turned 70 and did not retire, for a maximum of six, thus enlarging the Supreme Court from nine Justices to up to fifteen.
A firestorm ensued. Critics rightly called Roosevelt’s proposal a plan to pack the Court. Even liberals who deplored the Court’s decisions, including many congressional Democrats, opposed it.
Its arm cruelly twisted by Roosevelt’s threat to its independence, the Supreme Court began surrendering in self-preservation. On March 29, the Court upheld a revised Frazier-Lemke Act; the National Firearms Act; the Railway Labor Act, which promoted collective bargaining; and a Washington state law providing for minimum wages for women.
Then cases arose involving the blatantly pro-labor Wagner Act and the Social Security Act. The Court was in a hideous bind. Most of the Justices opposed the expansion of government power which these laws entailed – but if they voided them, Congress would probably enact Roosevelt’s Court pack.
On April 12, the Court upheld the Wagner Act. On May 18, Van Devanter announced his imminent retirement, enabling Roosevelt to nominate a Justice.
The case for his bill was weakening. But Roosevelt would not quit.
Such was the situation when the Supreme Court considered the Helvering v. Davis case.
There were three loopholes in the Constitution as it was written that, retrospectively, turned out to be keys in its subversion. Two were just loosely specified phrases that were readapted later ("interstate commerce" and "general welfare"). That sort of thing it would seem is inevitable; indeed the same sort of thing obtains around, for example, the second amendment; it's just that the 2nd cannot by its nature be used to justify much lawmaking; the interstate commerce and general welfare clauses can. But if they did not exist, then other loose phrases would have probably been found. And in any case, words don't enforce themselves, so overt loopholes or not, the Constitution is only as good as the people who enforce it.
The third fault line in the Constitution was a simple oversight that the founders should not have made: not specifying the size of the Supreme Court. The founders clearly understood that the Court had to be independent; that's why they gave life tenure and specified that their salaries could not be lowered while they were in office. But independence is clearly threatened by the ability to redefine the size of the Court. It is interesting to speculate what might have happened in the 30s had FDR not been able to threaten the Court. How much less socialism would we have today?