President Donald Trump in the Cabinet Room of the White House, December 13, 2018. Jim Young | Reuters

President Donald Trump enters 2019 facing threats to his presidency from all sides. Special counsel Robert Mueller continues his probe, which has resulted in convictions of three former top Trump aides. The stock market, Trump's barometer for his own success, is suffering its worst performance since the 2008 financial crisis. A quarter of the government remains closed. And on Thursday, Democrats will take the House of Representatives. But Trump's situation is not as dire as Democrats might hope, since his approval rating has stubbornly refused to budge. He remains exactly as overwhelmingly popular among Republicans as he was the first day of his presidency. Among the wider public, Trump remains unpopular — but not dramatically more so than many other modern presidents.

While his dismal approval rating was an outlier on the day he took office, it is now — while still in the low 40s — more or less within a typical range for a president at this point in a term. Other presidents started off popular only to quickly lose support as they quit campaigning and began to govern. Trump, whose leadership style is often criticized as erratic or unsteady, has remained steadily unpopular. It has been 712 days since Trump became president. That many days into his own presidency, President Ronald Reagan had less public support than Trump does, according to a tracker from the political science website FiveThirtyEight. President Barack Obama, whose first-day approval bested Trump's by more than 20 percentage points, was less than 5 percentage points more popular than Trump 712 days in. President Bill Clinton was less than 2 percentage points more popular. Of course, voters sent all three former presidents back to the Oval Office for a second term.

What it means for 2020

Trump's approval rating has taken on new significance with Sen. Elizabeth Warren's announcement on Monday that she had taken a formal step toward a 2020 run for president and other Democrats expected to announce their candidacy soon. As the race gains steam, the president's low numbers, combined with a devastating defeat for the GOP in the 2018 midterms, are being trumpeted among Democrats as bellwethers for the presidential race. WATCH: Who really won the midterms? Why both parties can claim victories

But unless it suddenly dips, the president's approval rating does not yet predict a defeat in 2020. Trump's approval, which has consistently been in the low 40s, amounts to a "political safe zone," according to Clifford Young, the leader of the global election and political polling risk practice at Ipsos. Research from Young and Chris Jackson, a vice president at the polling outfit, has shown that an approval rating of 40 percent would make Trump the narrow favorite for re-election. The two studied more than 500 elections to reach that conclusion. In 2015, Young's model predicted a Republican victory in the 2016 presidential race despite polling that gave Democrat Hillary Clinton the edge. To be sure, there are factors that could disrupt the president's approval. An economic downturn or an unpopular war could pose a threat unlike those the president has faced in his first two years in office. And presidents typically become less popular over time. In Iowa, a key electoral state, many Republican voters are telling pollsters they are willing to consider other Republicans. But, like so many other aspects of his presidency, Trump's ratings have not hewed to historical norms. His approval has not been subject to the same deterioration effect as previous presidents.

'Calm down and enjoy the ride'