(CNN) Impeachment is the fever dream of Democrats and progressives whose engagement brought Democrats into the House majority.

That's why one congressman pledged to re-introduce articles of impeachment as soon as possible, and another said she promised her son of the President, "we're going to impeach the motherf****r."

It's a topic that's been on Democrats' tongues since Trump took office. But newly elected House Speaker Nancy Pelosi and other Democratic leaders have argued against serious consideration of that option.

Controlling the urge to impeach could be Pelosi's most difficult challenge in her first months back in the Speaker's office.

Democrats really want to impeach Trump, but the country doesn't

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In a CNN Poll conducted by SSRS in December , 80% of Democrats said they thought the President should be impeached and removed from office. That's a strong tide for Pelosi to fight.

But the reason she'll fight it is expressed in the same poll, where just 36% of independents and 7% of Republicans said Trump should be impeached and removed from office.

Just 43% of the respondents at large said he should be impeached and half -- 50% -- said he should not.

Democrats want it. The country does not.

Impeaching Trump is different than removing him from office

Getting rid of a president using impeachment is a two-step process. The House investigates the president for high crimes and misdemeanors and votes to impeach. But it's the job of the Senate to hold a public trial and remove the president from office. And while Democrats seized control of the House and the power to impeach Trump, they actually lost a net of two seats in the Senate. It would take 67 senators to vote to remove a president from office in the Senate. There are 47 Democrats and two independents who usually vote with them. Unless and until a large number -- 20! -- of Republican senators are willing to vote to remove Trump from office, impeaching him in the House would only accomplish making impeachment the cause celebre of Trump and his supporters.

Pelosi noted this in an interview with USA Today when she said any impeachment effort should be heavily bipartisan.

"If there's to be grounds for impeachment of President Trump -- and I'm not seeking those grounds -- that would have to be so clearly bipartisan in terms of acceptance of it before I think we should go down any impeachment path," she said

Trump's approval rating is not at impeachment levels

That 43% support for Trump being impeached is nothing to sniff at -- it's on par with the 43% who said Richard Nixon should be impeached in March of 1974 , not long before he resigned to avoid impeachment. But Trump's approval rating is much higher than Nixon's at that time.

Granted, Trump's approval rating is much lower than Bill Clinton's at the time of Clinton's impeachment. But the Clinton lesson is one Pelosi probably remembers very well. Republicans' impeachment effort against Clinton backfired and his popularity actually grew as the process wore on. He also survived the trial in the Senate.

The real prize for Democrats would be winning in 2020

Democrats won't have a chance to strengthen their hand in the Senate until the next election in 2020, which also happens to be when Trump is up for re-election. Beating him and putting a Democrat in office is probably a much more tantalizing idea to someone like Nancy Pelosi than impeaching Trump. Her most recent comments on impeachment, made to NBC News just before she was sworn in as speaker, were interesting on this point, when she said no decision should be made until special counsel Robert Mueller delivers his report on the Russian election interference investigation.

"We shouldn't be impeaching for a political reason and we shouldn't avoid it for a political reason," she said

Impeachment takes a long time

If Democrats do ultimately move to impeach Trump, the process would be all-consuming and take a long time. The Starr report was released on September 11, 1998. The House voted to impeach Bill Clinton three months later on December 19, 1998. The Senate didn't acquit him until February of 1999

Nixon resigned rather than be impeached, but the process was taking even longer. Impeachment hearings against Nixon began in the House Judiciary Committee in May of 1974 and Nixon didn't resign until early August of 1974

It would be very hard for Democrats to find oxygen for any other political platform during that time.

Mueller could change everything you've just read

The important caveat in what Pelosi has said this week about impeachment is that Mueller has not yet completed his investigation or issued any kind of report. Key former Trump aides are still cooperating with the Russia investigation. Whatever Mueller finds could change the impeachment equation immediately and dramatically. Or not. That's why it's important to wait and see what he finds. There are plenty of Democrats who think there are already grounds to impeach Trump right now. But they are not, as described above, in the majority.

What Mueller's report, if and when it comes, won't change is the date of the next general election. And while Pelosi said Democrats shouldn't avoid impeachment for political reasons, the fact remains that if or until Republicans turn en masse against the President, it is probably a less attractive option for Democrats to pursue than making a political argument to voters.