Best and worst presidents are subjective to one owns personal political point of view and ideology. Most historians will tell you it takes 20 years after a president leaves office to actually rate or rank him. That give them time to gauge the long term effects of their policies on the nation. It also gives it time for the partisan effect to die down some. There's also chances historians will rank or rate a president differently than the general public. Time also changes a presidents rankings as more become known about them many years, decades after they left office.
Public perception, rankings can show some weird results especially when it come to political partisan ship. To the question who were the best and worst presidents since WWII, A Feb 2017 poll of the public placed Trump 5th best since WWII and the worst since WWII. That same poll placed Obama as 2nd best and 2nd worst right behind Trump. A march 2018 poll had Trump still the 5th best and the worst since WWII while Obama became 2nd best and remained 2nd worst.
Including for the first time President Donald Trump, a Morning Consult poll taken February 9–10, 2017, asked 1,791 registered voters in the United States, who they thought were the best and worst Presidents since World War II.
Best President since World War II:
Ronald Reagan (26%)
Barack Obama (20%)
John F. Kennedy (17%)
Bill Clinton (9%)
Donald Trump (6%)
George W. Bush (tie) (2%)
Harry Truman (tie) (2%)
Jimmy Carter (tie) (2%)
George H. W. Bush (tie) (2%)
Richard Nixon (tie) (1%)
Lyndon B. Johnson (tie) (1%)
Gerald R. Ford (<1%)
Worst President since World War II:
Donald Trump (26%)
Barack Obama (25%)
Richard Nixon (13%)
George W. Bush (7%)
Bill Clinton (6%)
Jimmy Carter (5%)
George H. W. Bush (3%)
Lyndon B. Johnson (2%)
Ronald Reagan (tie) (1%)
Gerald R. Ford (tie) (1%)
Harry S. Truman (tie) (1%)
John F. Kennedy (<1%)
2018 Quinnipiac poll
A Quinnipiac University poll taken March 3–5, 2018, asked 1,122 voters in the United States who they thought were the best and worst Presidents since World War II.
Best President since World War II:
Ronald Reagan (28%)
Barack Obama (24%)
John F. Kennedy (tie) (10%)
Bill Clinton (tie) (10%)
Donald Trump (7%)
Dwight Eisenhower (4%)
Harry Truman (tie) (3%)
Jimmy Carter (tie) (3%)
Lyndon B. Johnson (2%)
George H. W. Bush (tie) (1%)
Richard Nixon (tie) (1%)
George W. Bush (tie) (1%)
Gerald R. Ford (<1%)
Worst President since World War II:
Donald Trump (41%)
Barack Obama (21%)
Richard Nixon (10%)
Jimmy Carter (8%)
George W. Bush (6%)
Bill Clinton (4%)
Lyndon B. Johnson (tie) (2%)
Ronald Reagan (tie) (2%)
Gerald R. Ford (1%)
Harry S. Truman (tie) (<1%)
Dwight Eisenhower (tie) (<1%)
John F. Kennedy (tie) (<1%)
George H. W. Bush (tie) (<1%)
https://en.wikipedia.org/wiki/Historical_rankings_of_presidents_of_the_United_States
This shows in the general public rankings how one's partisanship, one's political affiliation can effect the rankings. Now how historians rank presidents can differ quite a bit from the general public's.
As for Trump, being ranked by historians, 20 years into the future, I agree. I think he'll be down near the bottom. But to be sure, we'll have to wait for a historian pol, ranking of the presidents 20 years hence.