For months, President Trump has claimed that U.S. Steel has announced plans to build more than six new plants. Throughout the midterm election, he repeatedly said that Democrats had signed onto an “open borders” bill. And he has long charged that millions of fraudulent votes were cast in the 2016 election.

None of these claims is true. What’s more, most Americans don’t believe them, according to a new Washington Post Fact Checker poll.

Fewer than 3 in 10 Americans — including fewer than 4 in 10 Republicans — believe these or several other prominent claims by the president, according to the poll.

[Read the full Post Fact Checker poll results]

The poll sought to determine what Americans believe — the truth or the president. The Post has never conducted this type of poll before and it serves as the most comprehensive examination of whether Trump’s false and misleading claims have taken root among the broader American public.

The survey included 18 pairs of opposing statements — one true, one false — without identifying who made the statement. Eleven questions gauging belief in false claims by Trump were mixed among four false claims by Democrats, a true claim by Trump and two probing other factual statements.

Test your ability to identify true claims from falsehoods said by Trump, Democrats and others Article continues below Source: Nov. 30-Dec. 10 Washington Post poll of 1,025 American adults with an error margin of +/- 4 percentage points.

Only among a pool of strong Trump approvers — about 1 in 6 adults in the survey — did majorities accept several, though not all, of his falsehoods as true.

False claims commonly made by Democrats are more widely believed than those made by the president. For instance, 46 percent of adults incorrectly believe there are more people in prison for selling or possessing marijuana than for all violent crimes, an assertion made by Massachusetts Sen. Elizabeth Warren in June. That compares with 22 percent who correctly said violent criminals were more common in ­prison.

Where Americans get their information is a significant factor in determining what they believe.

Among adults who say Fox News is one of their top two sources for political news, 33 percent believe in Trump’s false claims tested in the poll, on average, compared with 21 percent of those who say Fox is not a main news source.

Americans who count MSNBC and CNN as one of their top two news sources are somewhat more likely to reject Trump’s falsehoods but are also more likely to believe false statements made by Democrats. On average, 44 percent of MSNBC viewers and 40 percent of CNN viewers believe false Democratic claims, compared with 30 percent of those who say MSNBC is not a primary news source and 28 percent who do not primarily watch CNN.

People who say NPR or newspapers are one of their top two news sources are among the least likely to believe false claims by Trump, averaging 16 percent and 17 percent, respectively.

The poll finds that Americans see Trump’s rhetoric as distinctly inaccurate compared with other politicians and the mainstream media, which Trump regularly derides as “fake news.” While majorities say each regularly makes misleading statements, nearly half say Trump makes claims that are “flat-out false,” compared with less than one-third who say the same of Republicans and Democrats in Congress or of the mainstream media.

More than 6 in 10 Americans say they believe fact-checking organizations when they conclude that Trump has made a false claim. Just about half are confident in similar assertions in newspapers and on cable news.

Since becoming president, Trump has made 6,420 false or misleading statements through Oct. 30, including more than 4,400 this year, according to a database maintained by the Fact Checker.

Unlike many politicians who will abandon an untrue claim when fact-checked, Trump generally repeats his falsehoods. To capture this phenomenon, the Fact Checker this week introduced the Bottomless Pinocchio, a new category awarded to politicians who repeat a false claim so many times that they are, in effect, engaging in campaigns of disinformation. Fourteen of the president’s statements qualify for the list.

The Washington Post Fact Checker and Pollsters teamed up to find out how many Americans believe Trump’s frequently used false and misleading claims. (Meg Kelly/The Washington Post)

One of those — Trump’s assertion that he has started building his long-promised wall along the southern border, which he has said nearly 100 times — found little support in the poll.

The survey finds that 26 percent of Americans believe the statement, “Construction has begun on a wall along the U.S. border with Mexico.” About twice as many Americans, 51 percent, accurately selected the description that, “There is ongoing repair of fencing along the U.S. border with Mexico, but no wall is being built.” Roughly one-quarter said they were unsure.

Most of Trump’s base, however, believes that a wall is being built, with 56 percent of those who strongly approve of Trump’s job performance embracing that assertion.

Overall, 44 percent of Trump’s strongest supporters believe his false claims, while 35 percent of Republicans and 20 percent of Democrats believe them.

The Trump falsehoods people are most and least likely to believe A Washington Post Fact Checker poll asked Americans to choose between 11 false claims made by Trump and an alternative claim that was true. On average, 25 percent believed Trump's false claims. Strong Trump Approvers Democrats Republicans 20 35 44% Adults overall 25% Percentage who said each false statement was true instead of a parallel true statement (or saying they are unsure) The policy of separating parents and children who crossed the border illegally earlier this year was required by long-standing U.S. laws. 20 45 60 30 North Korea has done more to end its nuclear weapons program in the past six months than in the previous 25 years. 34 22 56 59 The United States funds the majority of the budget for NATO (North Atlantic Treaty Organization). 26 53 58 35 Construction has begun on a wall along the U.S. border with Mexico. 19 35 56 26 The global temperature has been increasing in recent decades because of natural causes, not human activity. 10 33 51 19 Russia did not try to interfere with the 2016 U.S. presidential election. 5 27 47 15 There is evidence that millions of fraudulent votes were cast in the 2016 presidential election. 26 28 37 The 2017 tax law passed by Congress was the largest tax cut in U.S. history. 25 29 33 U.S. military spending is currently at a record high level. 29 34 39 Democratic senators have signed onto a bill promoting an “open borders” immigration policy. 12 27 28 15 In the past year, the company U.S. Steel announced plans to build more than six steel plants in the United States. 14 17 25 Source: Nov. 30-Dec. 10, 2018 Washington Post poll of 1,025 U.S. adults with an error margin of +/- 4.5 percentage points. The Trump falsehoods people are most and least likely to believe A Washington Post Fact Checker poll asked Americans to choose between 11 false claims made by Trump and an alternative claim that was true. On average, 25 percent believed Trump's false claims. Strong Trump Approvers Dems Reps 20 35 44% Adults overall 25% Percentage who said each false statement was true instead of a parallel true statement (or saying they are unsure) The policy of separating parents and children who crossed the border illegally earlier this year was required by long-standing U.S. laws. 20 45 60 30 North Korea has done more to end its nuclear weapons program in the past six months than in the previous 25 years. 22 56 34 59 The United States funds the majority of the budget for NATO (North Atlantic Treaty Organization). 26 53 35 58 Construction has begun on a wall along the U.S. border with Mexico. 19 35 56 26 The global temperature has been increasing in recent decades because of natural causes, not human activity. 10 33 51 19 Russia did not try to interfere with the 2016 U.S. presidential election. 5 27 15 47 There is evidence that millions of fraudulent votes were cast in the 2016 presidential election. 26 28 37 The 2017 tax law passed by Congress was the largest tax cut in U.S. history. 25 29 33 U.S. military spending is currently at a record high level. 29 34 39 Democratic senators have signed onto a bill promoting an “open borders” immigration policy. 12 27 28 15 In the past year, the company U.S. Steel announced plans to build more than six steel plants in the United States. 14 17 25 Source: Nov. 30-Dec. 10, 2018 Washington Post poll of 1,025 U.S. adults with an error margin of +/- 4.5 percentage points. The Trump falsehoods people are most and least likely to believe A Washington Post Fact Checker poll asked Americans to choose between 11 false claims made by Trump and an alternative claim that was true. On average, 25 percent believed Trump's false claims. Strong Trump Approvers Democrats Republicans 20 35 44% Adults overall 25% Percentage who said each false statement was true instead of a parallel true statement (or saying they are unsure) North Korea has done more to end its nuclear weapons program in the past six months than in the previous 25 years. The policy of separating parents and children who crossed the border illegally earlier this year was required by long-standing U.S. laws. 34 22 56 59 20 45 60 30 Construction has begun on a wall along the U.S. border with Mexico. The United States funds the majority of the budget for NATO (North Atlantic Treaty Organization). 26 53 58 35 19 35 56 26 The global temperature has been increasing in recent decades because of natural causes, not human activity. Russia did not try to interfere with the 2016 U.S. presidential election. 5 27 47 15 10 33 51 19 There is evidence that millions of fraudulent votes were cast in the 2016 presidential election. The 2017 tax law passed by Congress was the largest tax cut in U.S. history. 25 29 33 26 28 37 Democratic senators have signed onto a bill promoting an “open borders” immigration policy. U.S. military spending is currently at a record high level. 12 27 28 15 29 34 39 In the past year, the company U.S. Steel announced plans to build more than six steel plants in the United States. Source: Nov. 30-Dec. 10, 2018 Washington Post poll of 1,025 U.S. adults with an error margin of +/- 4.5 percentage points. 14 17 25 See all false statements

The Post poll also suggests Republicans have grown less concerned about presidents being honest than they were a decade ago. In 2007, an Associated Press-Yahoo poll found 71 percent of Republicans saying it is “extremely important” for presidential candidates to be honest, similar to 70 percent of Democrats and 66 percent of independents. The new Post poll shows identical shares of Democrats and independents prioritizing honesty in presidential candidates, but the share of Republicans who say honesty is extremely important has fallen to 49 percent, 22 points lower than in the AP-Yahoo poll.

A separate question in the Post poll finds that clear majorities across party lines say it is never acceptable for political leaders to make false statements. But 41 percent of Republicans say false claims are sometimes ­acceptable “in order to do what’s right for the country,” while 25 percent of Democrats and 26 percent of independents say the same.

While belief in false claims by Trump is generally low, the public’s ability to identify a true alternative varied widely depending on the question, with many saying they were unsure which of the two statements were true.

Americans are most unsure about the false claim that U.S. Steel has announced plans to build more than six steel plants in the United States. Just 12 percent of adults say Trump’s claim is true, though fewer than one-quarter correctly identify the true statement that U.S. Steel has announced plans to restart two blast furnaces at one existing plant. Nearly two-thirds say they are unsure which claim is true.

On climate change, the survey shows fairly little debate. President Trump has repeatedly suggested global warming is a hoax, only recently backtracking to say he thinks it is occurring but not caused by humans. But 65 percent of adults endorse the accurate statement that the global temperature has been increasing in recent decades mainly because of human activity. By contrast, 19 percent endorse a statement saying that temperatures have been rising because of natural causes, not human activity. Again, strong Trump approvers are the outliers on this question, with 51 percent siding with the inaccurate statement.

One result from the survey suggests doubts about Trump’s honesty may lead some to be skeptical of him when he says things that are true. Trump often accurately says that the U.S. unemployment rate is at its lowest level in roughly 50 years, but less than half of adults, 47 percent, believe this is true.

Partisans do not always differ in their acceptance of inaccurate Trump statements. Thirty-nine percent of Democrats believe Trump’s oft-repeated statement that U.S. military spending is currently at a record high, narrowly higher than the 34 percent of Republicans who say this. Defense spending is currently lower than a recent peak in 2010, as well as during World War II in inflation-adjusted dollars.

Trump was particularly careless with the truth at his raucous 2018 campaign rallies. The Fact Checker evaluated two Trump campaign rallies in July and September and found at least 70 percent of Trump’s factual assertions were false or misleading.

The Post poll finds little connection between watching Trump’s rallies and believing his false claims. Americans who report watching rallies on TV or in-person are seven percentage points more likely than others to believe false claims made by Trump, but rally watchers are also six points more apt to accurately identify the true alternative claim to Trump’s falsehood.

The survey, completed Nov. 30-Dec. 10, was conducted among a random sample of 1,025 adults from NORC’s nationally representative AmeriSpeak panel. Overall results have a margin of sampling error of plus or minus 4.5 percentage points.

Emily Guskin, Meg Kelly and Salvador Rizzo contributed to this report.