2019 is shaping up as a year testing the Trump presidency on every front: foreign policy, trade, a potentially slowing economy, and relations with the Democratic-controlled House and an increasingly fractious Senate—eleven of whose Republican members just joined forces with Democrats to vote against lifting sanctions on a Russian oligarch.

Looming over all of this is the impending the Mueller report, along with aggressive Democratic oversight. A report whose credibility cannot be dismissed out of hand suggests that President Trump’s personal lawyer lied to Congress at his direction about his business dealings with Russia during the 2016 presidential campaign. The pressure on the president is intensifying, and according to a Pew Research Center report released today, Mr. Trump is in a weak position to withstand it.

Only 41 percent of Americans are confident that President Trump keeps his business interests separate from the decisions he makes as president, while 57 percent lack confidence that he separates them. If the special counsel finds evidence that the president’s business dealings in Russia spilled over into American foreign policy, a solid majority of the people will be inclined to believe it.

President Trump’s refusal to release his tax returns exacerbates this mistrust. Sixty-four percent of American say he should make them public, up 7 points since January 2018.

Even in this era of partisan polarization and mistrust of government, public doubts about their current president and his administration stand out. Fully 58 percent say they trust what Donald Trump says less than the utterances of previous presidents, and the public’s assessment of the ethical standards of top administration officials stands at record lows compared to administrations dating back nearly four decades.

These attitudes would be less dangerous for President Trump if the public had reached equally negative judgments about Special Counsel Robert Mueller. But this is not the case. Fifty-five percent of Americans are confident that Mr. Mueller is conducting a fair investigation into Russian involvement in the 2016 election. By contrast, only 37 percent believe that the president is handling matters related to the investigation appropriately.

Public confidence in the Special Counsel is deeply entrenched. Despite ongoing efforts by the president and his associates to discredit the investigation as a witch hunt, public approval of Mr. Mueller has not budged during the past twelve months, and the share saying they are “very confident” in him has increased.

Despite these negative views, President Trump enjoys about the same level of approval as he did a year ago, and Pew’s examination of eight different dimensions of public confidence shows why. Fifty-one percent of Americans believe that Mr. Trump will be able to negotiate favorable trade agreements with other countries, and 49 percent are confident that he will make good decisions about economic policy. But large majorities express a lack of confidence in his ability to perform the rest of his duties, including handling international crises, making wise decisions about immigration, and working effectively with Congress.

If President Trump strikes a trade deal with China and the economy continues to grow at a healthy pace, he may well retain his mediocre but remarkably stable public approval, and his party will stick with him. But if he plunges the United States into a trade war and the economy slows significantly, the bottom could fall out. He could find that a large number of Republican senators abandon him on critical issues, creating a veto-proof majority in the Senate. He could face a primary challenge for the Republican nomination. In the worst-case scenario he could find himself fighting impeachment by the House without solid Republican support in the Senate to protect him against conviction.

One thing is clear: as the pressure ratchets up, President Trump stands on shaky and potentially eroding ground.