By Robert Romano

Pollsters love to do general election matchup polls early in the process to figure out which candidates would fare the best against a sitting incumbent president like Donald Trump. The idea is to give primary voters of one party or another an idea of which candidate is the most “electable.”

For example, in April 2011, Democracy Corps published a poll that showed Mitt Romney could defeat then-President Barack Obama, 48 percent to 46 percent. In Oct. 2011, another CNN-Opinion Research poll showed Romney leading 50 percent to 45 percent.

But we all know how it turned out. Even after showdowns with House Republicans over the debt ceiling in 2011 — which resulted in budget sequestration that helped reduce the deficit — Obama went on to comfortably win re-election in 2012.

So, how much stock should we put in the Politico-Morning Consult poll that shows former Vice President Joe Biden at 42 percent versus President Donald Trump at 36 percent? Almost none.

The question, particularly for first term presidents, is whether voters think it is time for a change, or if they are willing to be patient while the incumbent party finishes what it started.

In modern history, since 1952, that has yielded a fairly high re-election rate for incumbent parties in their first terms. Dwight Eisenhower was re-elected in 1956, Lyndon Johnson won John Kennedy’s second term in 1964, Richard Nixon was re-elected in 1972, Jimmy Carter was ousted in 1980, Ronald Reagan was re-elected in 1984, Bill Clinton was re-elected in 1996, George W. Bush was re-elected in 2004 and Barack Obama was re-elected in 2012.

All told, in modern history, in 87.5 percent of the cases where the incumbent party had served one term it tended to be re-elected.

Readers will note that George H.W. Bush is not included in that listing. The reason for that is he won Reagan’s third term — that is, the third consecutive term that Republicans had held the White House. So, his being ousted in 1992 was less surprising because it came after 12 years of uninterrupted Republican rule in the White House. The same applies to Gerald Ford, who in 1976 was running for essentially Nixon’s third term, and Lyndon Johnson and then Hubert Humphrey in 1968 running for a third Democratic term.

But even if you include Bush and Ford in the mix as far as how sitting presidents have fared in a general election, in 70 percent of cases they have won since 1952. If you want to go back to World War II, Harry Truman won election in 1948 as a sitting president, and the number jumps up to about 73 percent.

If you look as far back as the beginning of the republic, sitting presidents who have stood for re-election in the general election have won about 70 percent of the time, although it is worth noting that until the 1800s, state legislatures generally chose electors.

So, there’s a distinct incumbency advantage, especially for first-term presidents that should give Trump an edge in 2020 no matter who the candidate is.

Particularly when it comes to presidents, in modern history, the American people, particularly independents, do not aspire to one-party rule. Swing voters tend to decide elections nowadays, and after just one term, they are still a lot more likely to give the incumbent the benefit of the doubt.

Where the rubber meets the road, and what separates one-term presidents from two-term presidents, will be the primaries. Biden or whoever is going to win the Democratic nomination must first compete and win the nomination, and do so in commanding fashion (rather than being bloodied along the way), to have a good chance to oust the incumbent.

Simultaneously, whoever the Democrat nominee is would need President Trump to have a bruising primary contest for the nomination to even out the odds. If Trump is vulnerable, it should be revealed in the primaries. But is William Weld really a credible threat to Trump? We’ll find out soon.

In modern history, unchallenged incumbents have tended to cruise to reelection. The likelihood of unseating an incumbent in the primary is close to zero, but real damage can be wrought to harm to his re-election chances. For more information, check out Stony Brook University Professor Helmut Norpoth’s primary model, which offers a guide to some of these trends. (Disclosure: I took his class!)

President Trump and Republicans have been in power for just two years and change. Is it already time for a change? History says the odds are not yet.

Robert Romano is the Vice President of Public Policy at Americans for Limited Government.