President Donald Trump's approval rating is underwater in several key battleground states ahead of the 2020 election, Morning Consult said in a new report.

Morning Consult found that Trump had a net-zero or negative approval rating in nine critical swing states, eight of which Trump carried in 2016.

Trump also maintained net positive — but still notably shaky — approval in solidly Republican states he carried by comfortable margins in 2016, Morning Consult found.

Nationwide, Trump had a 40% approval rating in May, down from 46% in April, according to Gallup, which cited growing calls for impeachment and the threat of new tariffs on Mexico as possible causes of the decline.

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President Donald Trump's approval rating is underwater in several key battleground states ahead of the 2020 election, Morning Consult said in a new report.

Morning Consult, which conducts daily surveys of more than 5,000 registered voters to track Trump's approval rating, found that Trump had a net-zero or negative approval rating in nine critical swing states that, except for New Hampshire, he carried in 2016:

Trump had a net approval rating of -19 in New Hampshire , with 39% approving of his job performance and 58% disapproving.

, with 39% approving of his job performance and 58% disapproving. He had a net approval rating of -13 in Wisconsin , with 42% approval and 55% disapproval.

, with 42% approval and 55% disapproval. In Michigan , Trump had a -12 net approval rating, with 42% approval and 54% disapproval.

, Trump had a -12 net approval rating, with 42% approval and 54% disapproval. Trump also had a -12 net approval rating in Iowa , with 42% approval and 54% disapproval.

, with 42% approval and 54% disapproval. He had a -7 net approval rating in Pennsylvania , with 45% approval and 52% disapproval.

, with 45% approval and 52% disapproval. In Arizona , Trump had a -6 net approval rating, with 45% approval and 51% disapproval.

, Trump had a -6 net approval rating, with 45% approval and 51% disapproval. Trump held a -4 net approval rating in Ohio , with 46% approval and 50% disapproval.

, with 46% approval and 50% disapproval. His net approval was also -4 in North Carolina , also with 46% approval and 50% disapproval.

, also with 46% approval and 50% disapproval. And Trump had a net approval rating of zero in Florida, with 48% approval and 48% disapproval (the margin of error for the state was plus or minus 1 percentage point).

Trump's net approval rating across the country, according to Morning Consult. Morning Consult

Trump also maintained net positive — but still notably shaky — approval in several solidly Republican states he carried by comfortable margins in 2016, Morning Consult found. He had a net +1 approval rating in Georgia, North Dakota, and Kansas (which had margins of error of plus or minus 1, 3, and 2 percentage points) and +3 net approval in Texas and Indiana (which had margins of error of 1 percentage point).

Nationwide, Trump maintained a 40% approval rating in May, down from 46% in April, Gallup polling found.

Gallup said Trump's dip in approval could be the result of several factors, including growing calls for the House to begin impeachment proceedings and Trump's threat of new tariffs on Mexico — largely unpopular with lawmakers — that has caused markets to plunge and could raise the cost of goods for Americans.

Read more: The Democratic base's support for impeachment has solidified after the release of the Mueller report

Despite Trump's poor approval in critical swing states, he still boasts strong support among Republican primary voters. Morning Consult's survey found that Trump had above 70% approval among every key demographic in the subset of potential GOP primary voters.

With 24 candidates running for the 2020 Democratic nomination in what is likely to be one of the most high-stakes and expensive presidential elections in recent history, Republican groups are gearing up to meet the enthusiasm from the Democratic side with outside spending and grassroots organizing.

The Great America PAC and the Committee to Defend the President, the two largest outside political action committees supporting Trump's 2020 reelection bid, told INSIDER in a Wednesday statement that they planned to join forces for a mass voter-registration drive aiming to register 1 million new voters in all the aforementioned battleground states.