If the government comes in to the situation, the price of bitcoin will even increase. The more coins that they buy, the more the price will increase. It becomes harder and harder for them to buy more bitcoins. That's the only way for the government to manipulate the bitcoin price other than spreading FUD about bitcoins. They have to accumulate bitcoins first before they can manipulate the price.
But who knows? Maybe the government has a huge part in the bitcoins of circulation. Maybe they bought the majority of bitcoins right from the start when it's still cheap so they can take down bitcoins at the right time.
Its not impossible for them to buy thousands of bitcoin using the money of the people but I don't think the government will try to get involve unless they can collect taxes to exchanges and bitcoin businesses in the country. Japan I think had made it possible. Tracking users who don't want to be tracked is a big problem.