Update: Minutes before the Senate's foreign relations committee was set to vote, Sen. Rand Paul (R-Ky.) announced he has changed his mind and will support CIA Director Mike Pompeo to be President Trump's secretary of state. That means, instead of making history for the opposition to his nomination, Pompeo is expected to get approval from the committee and be confirmed by the full Senate later this week.

It has been more than 70 years since a cabinet nominee had such a hard time making it out of the Senate while still being confirmed.

In at least one way, no secretary of state nominee has had as much trouble as CIA Director Mike Pompeo is having getting confirmed: By the end of the day Monday, he's expected to become the first secretary of state nominee to fail to get voted out of a Senate committee. But by the end of the week, he could be the first Cabinet member since 1945 to get a vote in the full Senate anyway.

There are a couple of factors that play off each other, making life hard for Pompeo and President Trump, but they mainly boil down to one: partisanship.

On Monday afternoon, Pompeo's committee approval vote is expected to fall short by one vote, as Sen. Rand Paul (R-Ky.) will join all 10 Democrats on the Senate Foreign Relations Committee to vote against Pompeo.

That's the first time that has ever happened to a secretary of state, said Matt Green, a political-science professor at Catholic University. While Cabinet nominations like the attorney general tend to have partisan confirmation processes, secretaries of state have generally received broad bipartisan support in the Senate, Green said.

That doesn't mean Trump has to go back to the drawing board. Senate GOP leaders are expected to bend procedural rules and bring Pompeo's nomination up for a full vote in the Senate, anyway, later this week.

There, with more votes in play, Pompeo is expected to narrowly gain confirmation, thanks to two Democrats who will make up for Paul's defection: Sens. Heidi Heitkamp (N.D.) and Joe Manchin III (W.Va.).

Heitkamp and Manchin are running for reelection in states that Trump won by double digits in 2016, so they have an incentive to be seen as working with the president. (Even though, notably, neither voted for Trump's premiere legislative accomplishment, the GOP tax overhaul, last year.)

Anyway. Back to our history lesson. If/when Pompeo does finally get confirmed by the Senate, he'll have done it in such a roundabout way as to make history again.

Green and Senate records say Pompeo is on the cusp of becoming the first Cabinet nominee to fail a committee vote since 1945. That time, Franklin D. Roosevelt's former vice president, Henry Wallace, couldn't get enough support from conservative Southerners in his own party to get through a committee vote to be commerce secretary, but he did get through the full Senate.

There are a couple of similarities between now and then that are instructive to understanding Pompeo's historic struggles:

Wallace was a Democrat who didn't make it out of a Democratic-controlled committee, thanks to factions within the party, Green pointed out. Pompeo is a Republican who probably won't make it out of a Republican-controlled committee for some of the same reasons. Paul represents a relatively small but vocal noninterventionist wing of the party.

It's like deja vu for Trump, who was extremely frustrated in the summer when an effort to repeal Obamacare failed by one vote in a Republican-controlled Congress because the party was so divided.

Pompeo also doesn't have the traditional résumé of a secretary of state. A congressman before he became CIA director, Pompeo doesn't have the relationship with senators or diplomatic experience on which most secretaries of state have been able to rely, Green pointed out.

That has led to skepticism among Democrats in particular that Pompeo may be swayed by Trump's controversial views on Russia and more nationalistic tendencies. At his confirmation hearing, he refused to explicitly say whether Trump asked him to get the FBI to back off an aspect of the Russia investigation.

It's also one reason many of Trump's nominees have struggled to get confirmed: They're often novices in the job. The secretary of state Trump fired for Pompeo, Rex Tillerson, had no government experience. He got approved by a 13-vote margin, which would be big for Pompeo but is remarkably tight, compared with previous secretaries of state. Green calculated that going back to the Carter era, secretaries of state were approved by an average margin of 91 votes.

There's a dynamic factoring into Pompeo's nomination that is uniquely 2018: hyperpartisanship when it comes to the president. Democrats voting against Pompeo have their policy reasons, but it's undeniable that the politics of sticking it to Trump are a winner among their base.

Opposing Trump is popular among Democrats because Trump is so extremely unpopular. His approval ratings have risen slightly, but he's still one of the most unpopular presidents in history at this moment in his presidency.

All of that combined makes Trump's life extremely difficult. His party has such a narrow majority in the Senate that losing one or two senators is all it takes to sink a key vote. He's nominating people for the Cabinet who would be controversial even in calmer times. And the Senate is so partisan right now that even the historically bipartisan secretary of state position is getting caught up in it.

“Need more Republicans!” Trump tweeted in frustration on Monday morning about the makeup of the Senate. On that, he's partially right. Pompeo's Senate snub will make history, but let's not forget it's happening, in part thanks to a Republican senator.