i think it was possible in past but now it is becoming difficult. because the users of bitcoin are now increasing and now it is becoming difficult for a single person to manipulate the price of bitcoin. in fact bitcoin is a decentralize currency and not under the control of any person or state.
That is not entirely true, it cannot be controlled by a certain person but it is controlled by the Chinese miners, it is true that bitcoin is decentralized but 70% of the user base is located in china and that makes them the ones who control the price if they decide not to sell or hold and that is what is happening now.
i will said maybe bitcoin price is manipulated by one group with larger of funds and they are trying to make panic in the market, because i see its happen on polo when dump and pump is already happen in almost one month ago. but they can not controlled bitcoin price as they want, because all things that happen in the market is because of the traders and people which want bitcoin price is up or down.