I do think we try very hard to keep it as guaranteed as possible, if something would happen to stocks as a whole the government is willing to pull a lot of stops
As a matter of policy, the government explicitly doesn't set policy in attempt to influence stock returns.
However, the government does try to prop the broader economy up. Rightfully so, because if that collapses you have people without jobs or rapid inflation. Neither of which are good for society.
It just so happens that stock returns are indirectly coupled to overall economic performance, so a healthy economy (generally) means a healthy stock market.