A new CNN/SSRS poll finds that former Vice President Joe Biden leads President Donald Trump 49% to 44% in a potential general election matchup. Matchups between Trump and other leading Democratic contenders (South Bend, Indiana, Mayor Pete Buttigieg, Vermont Sen. Bernie Sanders and Massachusetts Sen. Elizabeth Warren) are even closer.

Compared to polling taken back in October, the Democratic margin in all the head-to-heads has been cut by at least 5 points.

Public opinion on Trump has been remarkably stable throughout his presidency. His approval rating has mostly been stuck in the high 30s to low 40s, and he's consistently trailed his most likely Democratic opponent (Biden) in the polls by high single to low double digits.

But as we close out 2019 and head into 2020, it seems that Trump is gaining ground.

Beyond our poll, the average live interview poll shows significant movement toward Trump over the last two months. Biden's lead over the President in a potential matchup has dropped from 12 points to 7 points, which is still the largest advantage of any of the top Democrats against Trump. Trump picked up at least 4 points against the other leading Democrats since October.

In the 15 closest states of the 2016 election, where the presidential contest was decided by 8 or fewer points, Trump's in even better shape. None of the Democrats led in CNN's December poll. This follows other swing state polling suggesting that, just like in 2016, Trump could win the electoral college, while losing the popular vote.

The shift in Trump's favor nationally, not surprisingly, coincides with upward movement in his personal popularity. His net favorable rating (favorable - unfavorable) stood at -6 points among voters in CNN's latest poll. His net favorability rating in the two prior CNN polls that asked the question was -12 points.

The average poll also demonstrates that Trump is at the high end in his popularity. According to the FiveThirtyEight aggregate, this week Trump hit is highest approval rating among voters (45%) since March 2017.

Trump's upward trajectory is likely, at least in part, because of the economy. While most people have generally thought the economy is good, a booming 76% said it was good in the CNN poll out this week. That was the highest percentage since 2001.

Meanwhile, the impeachment of Trump doesn't seem to be making much of an impact on the polls. That could be because fewer voters say it's an extremely or very important issue to their vote than any other issue tested by CNN in November . Additionally, it could be because opposition to impeaching and removing Trump is higher than Trump's popularity ratings. This means more talk of impeachment may actually move Trump's approval rating up.

Another thing helping Trump is that presidential elections are not referendums. He's going to have a named Democratic opponent. None of the leading Democrats had a positive net favorability rating among voters in CNN's December poll. In October, all but Warren did. The drop in the Democrats' popularity could be because they're involved in a competitive primary, which is hurting their intra-party favorability ratings. None of the Democrats are anywhere near as popular among their own party's voters as Trump is with his. That could change once the primary ends, though.

Indeed, it's not like Trump is in a great position. The two most likely Democratic nominees, Biden and Sanders, are ahead of him by 7 points and 4 points respectively in the average poll. Most incumbent presidents have been leading their potential opposition at this point before the election.