There is no gas shortage...

Why is the dollar declining?

Lack of foreign investment in this country.
Its the opposite of the problem we had in the 80s, where U.S. dollars were buying Japanese cars and consumer goods but Japanese investors were buying dollar denominated assets and backing dollar denominated investments.
Now there are more attractive investments overseas. We keep buying foreign made goods but our money isn't coming back here, its staying overseas.

Our trade policy is killing us.

The doallar is declining because there are too many of them sitting out there in foreign hands. They are afraid to hold much more and are diversifying into other currencies and assets.

It's just supply and demand.

True, we don't produce enough in the way of consumer goods to soak some of those dollars back to US producers. But also our interests rates are low relative to other countries. This translates into a low rate of return on investments in the U.S.

Given the choice of parking those dollars here in US assets at, say, 3% annual return vs. 4 or 5% in Europe or Asia, what's your choice going to be?

It's not just trade policy. It's total complex of out financial, fiscal and trade policies that go beyond our means. Taken toghether they are choking the dollar.