A few links may provide some useful context for President Trump's actions on trade.
The U.S. International Trade Commission has a table that provides (at the far right column) the "ratio of values" — that is, the duties collected by the U.S. as a percentage of the total value of imports. From 2000 to 2017, that number has been somewhere between 1.7 and 1.4. The low was 1.2 in 2008 and the high was 1.7 in 2002. Compare that to the period from 1947 to 1979, which the left often idealizes (incorrectly, in my view) as the postwar boom of stable factory jobs before Reagan ruined everything with his income tax cuts and increased income inequality. From 1947 to 1979, that number was somewhere between 7.9 and 3.5. What it suggests is that tariffs levels now are so historically low that even if Trump winds up raising them as more than a temporary negotiating ploy, there's some room to maneuver.
J.P. Morgan Chase has a chart (on the second page of the three-page pdf) titled "A General Lack of Tariff Reciprocity." As that firm's Michael Cembalest put it, "there is an almost universal lack of trade reciprocity when it comes to tariffs applied BY the US, and tariffs applied TO the US; the former are lower than the latter. While there are other benefits from this state of affairs (access to low-cost consumer goods, higher corporate profits, pursuit of geopolitical objectives), the benefits and costs are most likely not equally distributed."
Finally, as a political matter, Democrats seem disinclined to criticize Trump on this. Here is a June 15 statement from the Senate Democratic leader, Charles Schumer:
Washington, D.C. – U.S. Senator Chuck Schumer released the following statement regarding the Trump administration's decision to impose new tariffs on Chinese imports:
"The president's actions on China are on the money. China is our real trade enemy, and their theft of intellectual property and their refusal to let our companies compete fairly threatens millions of future American jobs.
"While we await further details on this trade action, President Trump is right on target."
Now, conservatives may point out, acidly, that if they wanted a Chuck Schumer economic policy, they didn't need a Republican in the Oval Office. But as a practical matter, Trump has a lot more room to operate on this now than if he did if Schumer were out there denouncing every tariff as a job-killing tax increase that will raise prices on American consumers. As a congressman, Schumer voted against NAFTA.