"Politically, the striking outcome of the first year of the UPA government is its increasing vulnerability," Karat said in an article in the party organ "People's Democracy".
Prime Minister Manmohan Singh's government took office May 22 last year.
Karat said that in May 2009, when the UPA won the election but failed to get a majority in the Lok Sabha, the Congress leadership became complacent with the unilateral declaration of support by parties like the Bahujan Samaj Party (BSP), Samajwadi Party, Rashtriya Janata Dal (RJD) and Janata Dal-Secular (JD-S).
"By the end of the first year that complacency has been shattered. During the last budget session, the Congress had to adopt the tactic of bargain and striking deals to garner support from amongst these parties," he said.
Karat accused the government of failing to tackle the relentless price rise of essential commodities, particularly food items.
"This has been the biggest cause for people's suffering in the past year. For the poor, it has meant less food and more hunger and malnutrition," he said.
He added that this was the outcome of the government's decision to pursue neo-liberal economic policies.
"Food items and other essential commodities are traded and speculated in the market in a big way. The forward trading system is the playground for big trading companies and corporates.
"The government is in the least interested in curbing these interests who are making huge profits," he said.