According to the US Consitution, Article 1, Section 8, US Congress has the power "To declare War".
Currently, several mainstream news outlets are describing various tariff increases by the current US President as a "trade war".
Most recently, US Government labeled China as a "currency manipulator", and the current US President threatened to devalue the US Dollar. Similarly, the mainstream news articles are labeling such response as part of a potential "currency war".
Given the potential damage that could result from such wars, it seems that it would be in US Congress interest to limit the US President's ability to start and wage trade/currency wars.
Question: Does the US President not need approval from US Congress to start economic wars? If so, why not?