By Cokie Roberts and Steven V. Roberts

Does anybody here remember Blanche Lincoln? She was a two-term senator from Arkansas, a moderate Democrat who prospered in a red state by defying liberal power brokers like big labor.

The unions and ultra-left pressure groups went after her big-time in 2010, backing a primary challenge by Arkansas Lt. Gov. Bill Halter. She survived the primary — barely — but suffered mortal wounds in the process, then lost badly in the fall to Republican John Boozman.

We thought of Lincoln as the purist wing of the Democratic Party re-emerged this spring and threatened to run primary opponents next year against Sens. Joe Manchin of West Virginia, Heidi Heitkamp of North Dakota and Joe Donnelly of Indiana. Their sin: daring to support President Trump’s nominee for the Supreme Court, Judge Neil Gorsuch.

As one of those purist pressure groups, We Will Replace You, said in its manifesto: “The next crucial step is escalating our demands and demonstrating that we won’t accept anything less than full opposition — by showing Democrats just how many people are willing to back primary challenges to Democratic collaborators and enablers of Trump.”

This harassment is beyond stupid. It’s suicidal.

Democrats are struggling to win elections and have lost control of both Congress and the White House. Trump won West Virginia by 67 percent, North Dakota by 62 percent and Indiana by 56 percent.

The only Democrats who could possibly hold Senate seats in those states are ones like Manchin, Heitkamp and Donnelly: moderates who separate themselves from the rigid tenets of liberal theology. Lincolnizing them, purging them as heretics, would have only one result: making it easier for Trump and his congressional allies to retain power.

Look at the facts. Yes, Hillary Clinton won the popular vote by almost 3 million, but that’s a highly misleading figure, based entirely on huge Democratic margins in a few coastal and urban enclaves. In California alone, Clinton rolled up a lead of 4.3 million; in New York, it was 1.7 million. Take away those two states, and Trump’s national margin was above 3 million.

Trump won about 84 percent of the counties in America; Clinton, 16 percent. Only 26 percent of voters identified as liberals in Election Day exit polls, with 39 percent calling themselves moderates and 35 percent conservatives.

Add the nature of the American system: House members represent individual districts that are often gerrymandered to protect the party in power; each state gets two senators, no matter its size; and the Electoral College determines the president, not the popular vote.

The math is undeniable and unrelenting: Democrats cannot take back the White House or Congress simply by building up large majorities in Brooklyn and Boston. Politics is always about addition, not subtraction. Condemning moderates as “collaborators” and “enablers” will condemn the party to permanent minority status.

Groups like We Will Replace You are directly connected to Bernism, the mass mania that infected liberals during the Democratic primaries. They deluded themselves into believing that a self-proclaimed Democratic socialist, mouthing totally unrealistic slogans like “free college tuition,” could actually win.

Sure, Bernie Sanders backed Clinton after the conventions, but he stayed in the primaries far too long and convinced far too many of his followers that she was a flawed candidate not worth voting for. Yes, Clinton was a poor candidate, but without a doubt, Sanders helped elect Trump. He Lincolnized Clinton.

The fallout from Bernism is not just bad for the Democrats; it’s bad for the country. Moderates like Manchin, Heitkamp and Donnelly are an essential part of a functioning Senate. They are the dealmakers, the conciliators, the lubricators who make the legislative machinery run. Their shrinking numbers help explain why the Senate is imploding over Gorsuch’s nomination to the high court.

In 2005, a group called the Gang of 14 — seven Democrats, seven Republicans — brokered a pact over judicial nominations that avoided a partisan showdown. Only three of those 14 senators, all Republicans, remain in office. All the Democrats are gone, including four moderates from red states: Robert Byrd of West Virginia, Ben Nelson of Nebraska, Mark Pryor of Arkansas and Mary Landrieu of Louisiana.

There was no deal this year, comparable to the one forged 12 years ago, because there are so few dealmakers left.

If the Democrats forget Blanche Lincoln, if they insist on purging anyone who strays from liberal orthodoxy, they will misread — once again — the nature of the American electorate. And they will weaken, not strengthen, their ability to resist Trump.

Steve and Cokie Roberts can be contacted by email at stevecokie@gmail.com.