On one hand, you can look at this and wonder why anyone would want to undertake the incredible expense of a sub oceanic tunnel across the Bering Strait. What, with Anchorage already housing one of the world's busiest international airports, particularly for cargo aircraft.
However, completion of such a tunnel would have profound, long-reaching consequences, both negative and positive:
Chinese manufactured goods would presumably have shipping time cut in half. Even given the considerable distances, a 2km long freight train maintaining 110 km/h is a wee bit faster than a stacked & loaded Maersk container ship wallowing across the girth of the Pacific at a leisurely 20 km/h, and those trains can be run back to back separated only by a few km with basic logistics tools.
Rail and Trucking distribution arteries from Alaska down to the lower 48 would become among the busiest in the world.
American manufacturing jobs would be murdered. Already bled nearly to death, the ability to Skype an engineer in Guangdong, email schematics and have 14 boxcars of finished goods on your back dock in less than 2 weeks would be a deathblow to a lot of American jobs.
The economies of the U.S. and China would become increasingly tightly woven together, possibly creating a stabilizing effect diminishing the possibility of armed conflict - essentially the draft purpose of the European Union, after Germany went out on two world tours. The U.S. would be the loser in this scenario, as Chinas ascendancy would only continue on the world stage, while the U.S. ability to project and maintain power would suffer in the face of a diminished economy.
Americas incredible military would become unaffordable, and go through many rounds of contractions, until the U.S ends up a peer to countries like Russia or combined UK, FR and Germany - regionally powerful, globally insignificant.
So essentially this tunnel represents another step in a trade arrangement largely favoring only one partner, leading the other to contract, economy foundering, military eventually becoming unsustainable at current levels, heading into France-like levels of global insignificance excepting cultural impact.
Rome 2.0