President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE's approval rating among men has been slowly declining in recent months, according to an analysis of Hill-HarrisX public opinion data.

Since July of last year, male voters contacted for Hill-HarrisX surveys have become less likely to say they approve of how the president is performing his official duties. In the most recent poll, 48 percent of male respondents said they approved of Trump, a statistically significant decline from the the mid-50 percent ratings he received from men last summer.

The president's decline among male voters in Hill-HarrisX surveys began about the same time that Trump initiated a partial shutdown of the federal government in late December.

Before that time, most male respondents had given Trump positive job performance ratings.

Since the shutdown began, however, the president has received majority support from men in only one survey, Jan. 10.

Trump's job approval ratings among women have been more uniform over time.

The majority of female registered voters contacted by Hill-HarrisX have consistently given the president negative marks since the surveys began in July of last year. He has consistently received about a 43 percent positive rating, according to the data.

The president's slowly declining numbers among men in Hill-HarrisX polls have been reflected in his overall numbers.

Last summer, Trump's approval rating among all voters was consistently in the upper 40s; recently, voters have given him approval ratings in the mid-40s.

The Hill-HarrisX poll has been conducted every two weeks since the end of July 2018 among statistically representative samples of 1,000 registered voters with an overall sampling margin of error of 3.1 percentage points. The sampling margin of error for men and women is 4 percent.

Trump's slowly declining support fits into a general historical pattern observed in past administrations.

Aggregated polling data collected by the University of California—Santa Barbara shows that most presidents slowly lose support during their time in office. Those who have been elected to a second term usually manage to increase their support during their campaigns, however.

There's still more than a year to go before the 2020 general election but Trump will have to do something to reverse his approval rating trend in order to win reelection, Lee Miringoff, director of the Marist Poll told Hill.TV.

"When people ask about are you definitely going to vote for him, are you definitely going to vote against him, realistically, you got to be at least in the 40s, mid-40s on that question, and he's sort of in the low 40s," he said told "What America's Thinking" host Jamal Simmons.

Recent public opinion polls have shown Trump losing to several potential Democratic rivals, including former vice president Joe Biden Joe BidenOmar fires back at Trump over rally remarks: 'This is my country' Trump mocks Biden appearance, mask use ahead of first debate Trump attacks Omar for criticizing US: 'How did you do where you came from?' MORE, Sens. Kamala Harris Kamala HarrisButtigieg stands in as Pence for Harris's debate practice First presidential debate to cover coronavirus, Supreme Court Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (D-Calif.), Elizabeth Warren Elizabeth WarrenHarris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda Judd Gregg: The Kamala threat — the Californiaization of America GOP set to release controversial Biden report MORE (D-Mass.), and Bernie Sanders Bernie SandersButtigieg stands in as Pence for Harris's debate practice Bernie Sanders warns of 'nightmare scenario' if Trump refuses election results Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (I-Vt.).

But winning more votes nationally is no guarantee of the presidency, of course. In the 2016 election, Trump received 46.1 percent of the vote compared to Clinton's 48.2 percent.

—Matthew Sheffield