It is true that the Carter Center did not praise aspects of the elections in Venezuela as they had in previous elections, especially under Hugo Chavez.
To the issue of the National Assembly, Venezuela’s Supreme Court announced in March 2017 that it would assume the functions of the National Assembly because the Assembly was in “contempt of court” in March 2017.
Opposition leaders in the National Assembly violated a Supreme Court order by swearing in deputies who were barred from taking office. Three delegates were under investigation for allegedly buying votes during an election.
The National Assembly tried to swear in the three lawmakers multiple times in 2016. In January, they flouted the order and then removed them from power. They did it again in July. In November, the lawmakers allegedly resigned, but weeks later, they were back in the Assembly.
It certainly helped the opposition create a perception that there was a constitutional crisis, but the Supreme Court no longer wanted to tolerate the defiance of officials in the opposition.
Additionally, the opposition passed a number of laws in 2016 that were unconstitutional. These laws included an amnesty law and a law to privatize social housing. They were laws the Supreme Court would immediately throw out.
To your argument — “It is not the sanctions as people keep repeating, it’s them,” that simply is not true.
As Mark Weisbrot of the Center for Economic Policy and Research has made clear, sanctions imposed in 2017 “made it virtually impossible for the Venezuela government to take the measures necessary to eliminate hyperinflation or recover from a deep depression.” It made it exceptionally difficult to engage in “debt restructuring” or create a “new exchange rate system (Exchange Rate Bases Stabilization), in which the currency would normally be pegged to the dollar.”
From a story published at Foreign Policy in 2018 about sanctions that was written before Juan Guaido appointed himself president of Venezuela:
Venezuelans have good reason to be concerned that ordinary people will ultimately pay the price for sanctions. Recent data show that in the two months after Trump imposed financial sanctions, imports tumbled an additional 24 percent, deepening the scarcity of basic goods and lending credibility to the government’s argument that U.S. policies are directly harming Venezuelans.
In the last year, sanctions blocked 300,000 doses of insulin, $1.65 billion for food, and $7 million worth of dialysis supplies, according to former UN special rapporteur Alfred de Zayas.