It would be fascinating to dive into why comparisons between the administration of President Trump and that of Richard Nixon are so numerous. There are the obvious reasons: a president under investigation by a special counsel; questions about how a campaign might have been manipulated illegally. More broadly, though, part of the desire to compare Trump with Nixon is simply that it is the only example of a very specific occurrence. Nixon is one of the two most recent occasions in which a president has faced a significant impeachment threat, resigning before that threat could be realized. Is the progression of the investigation into Trump headed down a comparable path?

At CNN on Sunday, Harry Enten pointed to a new poll from Marist College showing that Trump is now viewed as negatively by Americans as Nixon was at the time he resigned in August 1974.

“Trump is as strongly disliked as President Richard Nixon was when he resigned the presidency 44 years ago this week,” Enten wrote. “Back then, 45% of people said Nixon was doing a poor job as president in a Harris Poll.” That matches Trump’s rating in the Marist poll.

While that bit of data attracted attention for the reasons outlined above, Enten adds an important caveat that often goes unnoticed when comparing Trump to Nixon.

One remarkable aspect of Trump’s approval rating is how steady it has been. In Gallup’s polling, Trump’s approval rating has never been more than five points away from 40 percent, sometimes 5 points above, sometimes below. While presidential approval ratings have often not moved much in the first year, Trump’s is unusually steady.

The next-smallest amount of movement? Nixon.

What often happens is that presidents come into office with relatively broad support that then fades. Trump came into office as unpopular and hasn’t improved on that much since.

You can see the more typical trend looking at nine of the last 10 presidents. (We skipped Gerald Ford because — no offense to the late president — his numbers weren’t worth including if it meant breaking up our nice three-by-three square.)

Most presidents, including Trump, saw at least some dip in their approval ratings after taking office. George W. Bush saw a slight decline, but his first year in office was marked by the huge surge in approval after 9/11.

Nixon’s poll numbers are interesting. He cruised to reelection in 1972, and, at first, many Americans took the Watergate revelations in stride. His approval sank in 1973, hitting a floor in the mid-20s in 1974. Eventually, senior congressional Republicans traveled to the White House to tell Nixon that support on Capitol Hill had softened and that he would lose an impeachment vote. Nixon announced his resignation the next day.

And that is the main difference. Yes, Trump is as disliked as Nixon. But the gap in views of Trump by party is far, far broader than it was for Nixon — even at the end of his tenure.

The gap in opinions of the president by party was under 40 points for most of Lyndon Johnson’s presidency. Under Nixon, it never topped 50 points. Under Ronald Reagan, it peaked at 70. Under George W. Bush, it at one point topped 80.

Under Trump, it has never been less than 70.

In other words, the gulf between how Republicans feel about Trump and how Democrats feel about Trump has always been at least 20 points wider than it was during Nixon’s administration. That’s one key reason Trump’s approval ratings have been so steady — and are still so much higher than Nixon’s were at the lowest point of his presidency.

Democrats hate Trump more than they hated Nixon. The lowest approval rating Nixon ever saw from Democrats was 11 percent — right as he was leaving office. More than 11 percent of Democrats have approved of Trump in only two weeks of Gallup polling, including his first week in office.

Republicans love Trump more than they loved Nixon. While Nixon’s approval several times topped Trump’s among Republicans, Trump’s approval has never been lower than Nixon’s average of 74 percent in Gallup polling.

That, of course, is why Republicans on Capitol Hill aren’t headed to the White House to tell Trump that he’s in trouble. Trump isn’t in trouble, in part because there hasn’t been the sort of smoking gun on the Russia investigation that the release of Oval Office recordings were for Nixon. But more broadly, Trump’s base stands with him strongly, and congressional Republicans aren’t interested in bucking that base.

We can put this another way: One reason that there are comparisons to Nixon in terms of polling is that partisanship means that his approval is lower than past presidents in the first place. Democrats hate Trump and that drives down his approval to Nixonian levels just as it drives up his disapproval. Just as Republicans are standing with Trump more than they stood with Nixon, Democrats are standing in opposition to him more fervently than they did to Nixon.

In many ways, Nixon’s and Trump’s presidencies are echoes of one another. But Trump is serving in a period where partisanship is much sharper. And that has colored and will continue to color how the country reacts to what he does — and what special counsel Robert S. Mueller III finds.