Though the US is not the sole cause of many problems, they certainly go out of their way to make many of them worse. In Venezuela, they've placed crippling sanctions on the country for years, and promoted political instability by openly backing numerous coups.
Sanctions are a neutral policy, like Google pulling out of China. The US is holding back from interfering in Venezuela (only supporting the constitutionally elected leader) and also refusing to participate in the suffering of the people.
Maduro has always allowed aid into the country. He refused aid from the US as they have a history of using such aid to import weapons and such. Most humanitarian groups immediately chastised the US for even trying to send aid in that manner, both because of their history and that it's hard to take their offers in good faith while they simultaneously withold $11 billion of Venezuela's oil proceeds.
The U.S. is imposing sanctions on Venezuela, to the effect of millions of dollars a day lost. As part of the sanctions, the U.S. has also seized hundreds of millions of dollars of Venezuelan assets in foreign bank accounts. There is a direct cause and affect between U.S. policy and life in Venezuela.
This is from an analysis from January last year when Trump announced additional sanctions on Venezuela:
"An even more problematic idea driving current U.S. policy is the belief that financial sanctions can hurt the Venezuelan government without causing serious harm to ordinary Venezuelans. That’s impossible when 95 percent of Venezuela’s export revenue comes from oil sold by the state-owned oil company. Cutting off the government’s access to dollars will leave the economy without the hard currency needed to pay for imports of food and medicine. Starving the Venezuelan economy of its foreign currency earnings risks turning the country’s current humanitarian crisis into a full-blown humanitarian catastrophe."
Ref. https://www.nytimes.com/2019/02/08/world/americas/venezuela-... https://www.aljazeera.com/news/2019/02/sanctions-venezuela-i...