Norms, we are told, matter. Violating norms, recklessly disregarding norms -- these are charges on which President Donald Trump is often arraigned in the court of public opinion.

The indictment starts with his annoying habit of inventing insulting nicknames for his opponents and critics. You can add to the list as you will and perhaps come up with enough names for a 700-plusword newspaper column.

But Trump hasn’t been the only one disregarding norms of late. Consider the question of whether and when the president and Senate should fill the Supreme Court seat vacated by Justice Ruth Bader Ginsburg.

The historic precedent is clear, as set out by National Review’s Dan McLaughlin. When a vacancy occurs in a presidential year and the opposition party has a majority in the Senate, the president can nominate, but the nominee almost always isn’t confirmed.

There have been 10 such vacancies in the history of the republic. Presidents made pre-Election Day nominations in six cases, but only one nominee was confirmed before the election. That was back in 1888.

Presidents whose parties had Senate majorities selected nominees in election years 19 times, and 17 of those nominees were confirmed. One of the two rejections came in 1968, when President Lyndon Johnson’s nominee for chief justice, Abe Fortas, was blocked by a bipartisan filibuster.

Senate Majority Leader Mitch McConnell thus was following precedent when he blocked consideration of Barack Obama’s nominee to fill Antonin Scalia’s seat; he is also following precedent by promising a floor vote on Trump’s nominee to fill Ginsburg’s.

It is Democrats who are inconsistent here. If you think a president’s nominee is entitled to a vote from an opposition Senate, then, a fortiori, you think she’s entitled to a vote from his own party’s Senate.

You may not think such flip-flopping violates a norm. But Democrats’ threats to pack the Supreme Court with additional justices if they win the presidency and a Senate majority certainly does.

The Supreme Court has had nine justices since 1869. After his landslide reelection, President Franklin Roosevelt tried to add up to six more in 1937. That was soundly rejected, even though his Democrats had a 76-16 majority in the Senate and a 334-88 majority in the House.

Another assault on institutional norms is Democrats’ proposal to admit Washington, D.C., and Puerto Rico as new states, though neither meets long-established requirements for new statehood, as I argued in The Washington Examiner last week.

A third is to somehow abolish the Electoral College on the grounds that it and the Senate are unfairly tilted in favor of Republicans. But, currently, each party holds 10 of the 20 Senate seats in the 10 largest-population states and 10 of the 20 Senate seats in the 10 smallest-population states. Not much of a tilt!

Similarly, any Electoral College tilt to Republicans is of short duration. In both 2004 and 2012, incumbent presidents were reelected with 51% of the popular vote. But that netted Democrat Barack Obama some 332 electoral votes and Republican George W. Bush only 286.

Hillary Clinton’s edge in popular votes came from California. That’s because, since 2000, for the first time since 1820, our largest-population state is voting far out of line with the national average.

That puts the party favored there at a disadvantage, just as a party whose votes are heavily clustered in relatively few congressional or legislative districts is at a disadvantage compared with a party whose votes are more evenly spread around.

Democrats can try to compensate for this by changing or evading the Constitution, but amendments must be approved by 38 state legislatures -- and 50 if they eliminate states’ equal representation in the Senate.

A more practical and speedy response, and one that doesn’t violate norms, is to modify your political positions and rhetoric. It may satisfy liberals’ pride to pile up votes in California and the coastal Northeast by denouncing deplorables in the flyover states. But it’s also feasible to win more votes there.

It was done in the 1990s. Bill Clinton twice carried nine of the 10 states touching on the Mississippi River, carrying their electoral votes 95-7. In 2016, Hillary Clinton lost eight of 10, 65-30.

Meanwhile, Brookings scholar Shadi Hamid in The Atlantic forecasts that if Trump wins, Democrats “will be unwilling, even unable, to accept the result ... resulting in more of the social unrest and street battles that cities including Portland, Oregon, and Seattle have seen in recent months.” Doesn’t post-election violence violate norms?

Michael Barone is a senior political analyst for the Washington Examiner, resident fellow at the American Enterprise Institute and longtime co-author of The Almanac of American Politics.