A Washington Post op-ed by Sen.-elect Mitt Romney (R-Utah) criticizing President Trump on the day before the new Congress convenes sparked a quick and sharp rebuke from the president and his allies on Wednesday.

But an article by a senator who is on his way out of the chamber provided perhaps an even more pointed critique of Trump.

In a Washington Post op-ed, Sen. Lamar Alexander (R-Tenn.) urged Trump to emulate his predecessor Barack Obama in negotiating with Democrats to end a partial shutdown of the federal government and secure funding for his long-promised border wall.

The senator, who has announced that he will not seek reelection in 2020, cited his negotiations with Obama on revising the No Child Left Behind law four years ago as an example for Trump and congressional Democrats to follow.

“First, Democrats should recognize now, as I did with Obama in 2015, that if an elected president has a legitimate objective, they should bend over backward to accommodate it — if they want a result,” Alexander said in the piece. “As for President Trump, he should be specific and reliable, as Obama was in 2015 when he told us he needed three things, and, after Congress passed legislation that included the president’s requests, he signed the bill into law.”

On the same day that Alexander’s op-ed was posted, Trump held a meeting with his Cabinet at which he delivered a message that was at odds with a proposal Vice President Pence made to Democrats last month to try to resolve the shutdown.

That proposal, which Democrats rejected, reportedly included $2.5 billion in funding for a wall along the southern border. But Trump said Wednesday that he would not accept such a figure, once again reiterating his demand for $5.6 billion.

In his op-ed, Alexander, who unsuccessfully ran for president in 1996 and 2000, proposed a trio of potential solutions to the standoff. He also rebuked lawmakers and the White House for allowing their stalemate over thes border wall to trigger a federal government shutdown that is now in its second week.

“Government shutdowns should be as off-limits to budget negotiations as chemical weapons are to warfare,” Alexander said. “Nevertheless, we are stuck in one. Resolving it by going Real Big on immigration could be Trump’s Nixon-to-China, Reagan-to-the-Berlin-Wall moment in history.”