Not harder to move up. It is easier to stagnate.
The slow 50 year growth of Johnsons Great Society war on poverty has only made things worse. The politics of poverty have breed generations of Americans to be dependent on the government and lose the will to acheive.
It needs to be noted that the largest sudden growth of the US middle class happened after Clintons welfare reform pushed millions of people off the dole and into jobs. Almost over night the middle class grew as income rose above that provided by welfare.
3 key indicators moved from that historic legislation being put into law. Average household income went up across all demographics, home ownership went up across all demographics and the long term unemployment rate fell.
Sadly almost all of those welfare changes were phased out during the Bush years as part of budget compromises with democrats to fund the wars in the Middle East.
The last remnant, the job requirement, was virtually eliminated by President Obama with an Executive Order allowing states to ask for waivers. Notorious welfare states like NY, Massachusetts and California quickly submitted requests for waivers with local politicians hoping to buy votes with benefits before the November elections.
