One of the hallmarks of the Trump presidency is that no matter how unpredictable and erratic he may be, opinions of him are incredibly stable. At this point in 2019, for example, the FiveThirtyEight tracker showed President Trump's job approval rating at 41percent, with 55 percent saying they disapproved of the job he was doing as president. Today, he clocks in at 42 percent approve to 53 percent disapprove. Plus ça change, plus c'est la même chose.

The good news for Trump: He has a durable floor. Even as the country is divided on impeachment, support for him has not collapsed. The bad news: He has a low ceiling. Even as approval ratings of his handling of the economy continue to tick up, they aren't translating into broader support for his presidency. The most recent Quinnipiac poll showed 57 percent of Americans happy with the job Trump was doing on the economy — the highest showing of his presidency. However, his job approval rating was 14 points lower at just 43 percent.

The other important reality of this era is the degree to which national polls have become less helpful in assessing Trump's electoral college strength. A president sitting at 42 percent approval, with "strong disapproval" outweighing "strong approval" by 10-12 points is not going to win the national popular vote. But, that doesn't mean he can't win the Electoral College.

And, in assessing the Electoral College reality, there's no better place to check into than Wisconsin. It is ground zero for 2020. And, for a good reason. Trump won the state by a little over 22,000 votes. In 2018, Democrat Tony Evers defeated GOP Governor Scott Walker by just 29,000 votes. And, while President Obama had little trouble winning the state in 2008 (12 points) or 2012 (7 points), then-Senator John Kerry carried the state in 2004 by just 11,000 votes.

Even if the Democratic nominee manages to hold all the states Hillary Clinton won, and win back Pennsylvania and Michigan, they can't get to 270 without adding Wisconsin (or picking up Arizona, a state Clinton lost by almost four points). Trump can't afford to lose Wisconsin either — unless he's able to pick up neighboring Minnesota — a state where he came within 44,000 votes back in 2016.

The most recent Marquette University Law School poll found a similar level of stability in opinions of President Trump that we see in national polling. His job approval in the state was 48 percent approve to 49 percent disapprove — not much different from his December showing of 47 percent approve to 50 percent disapprove. But, Charles Franklin, the Marquette pollster, notes that it "is the first time Trump's disapproval has fallen below 50 percent in the Marquette Law School Poll since March 2017 when 47 percent disapproved."

If President Trump were sitting at a 48 percent job approval rating nationally, there'd be every reason to see him as both the popular and electoral vote favorite. It's a lot easier to get to 50 percent from 48 percent than it is from his 42 percent (his current national average).

There's also the question of whether all the attention that has been given to impeachment has actually helped to shore Trump's support up a bit. Instead of the media and congressional Democrats focused on the more broadly unpopular things Trump has done — repealing Obamacare, the tax cut bill, or child separation at the border — their focus has instead been trained on the process of impeachment and partisan squabbling over rules, procedures and witnesses. For voters who are passive participants in politics — or who are not as strongly identified with a party — the impeachment debate has been background noise. And, it has allowed things like the good economy to come into view.

Even so, just as we've seen in national polls, opinions of Wisconsin voters on Trump's handling of the economy (55 percent approve) are 7-points higher than his overall job approval rating. And, in head to head matchups, Trump trails both former Vice President Joe Biden (45 to 49 percent) and Senator Bernie Sanders (46 to 47 percent). And, as CNN/Atlantic Media's Ron Brownstein found, 14 percent of those who approved of the job Trump was doing on the economy were supporting Biden. For Sanders that number is 12 percent. In other words, the idea that a good economy will help 'rescue' Trump from his bad behavior isn't showing up in the numbers. In a state that will be decided by such a narrow margin, Trump can't afford to lose the voters who are actually giving him credit for his work on an issue as big and essential as the economy.

Marquette pollster Charles Franklin also wonders if the Democratic primary and the lack of a known nominee is giving Trump something of a short-term sugar high. In an email, Franklin told me that in combined data from the last four Marquette polls, he found that those who said they disapproved of Trump are more likely to answer "neither" or "don't know" when asked to choose if they'd vote for Trump or a named Democrat than do those who approve of the job Trump is doing.

Democrats, Franklin writes to me, "are not terribly divided over their candidates, but if the Democrat [they like] is a 2nd or especially 3rd or 4th choice, some grumpy Dems [when asked if they'd vote for Trump or vote for a certain Democrat] say 'neither.'"

Overall, says Franklin, "I'm reading that as the disapprove Trump people are not united on an opponent, whereas the approvers are mostly strong for Trump. I'm betting that as a Dem nominee emerges we'd see the neither and don't know go down and that should boost the Dem vote a bit."

As we head into month four since Speaker Nancy Pelosi called for Congress to open an impeachment investigation into President Trump, overall opinions of the president have not changed all that much. That's both good news and bad news for him. He hasn't gained political ground, but his 48 percent job approval rating in the critical state of Wisconsin suggests that he's not losing it either. But, the fact that a good economy isn't translating into votes suggests that voters' opinions of him are impervious to good news too.

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