(CNN) On Thursday, when news of the killing of Iranian commander Qasem Soleimani broke, Massachusetts Sen. Elizabeth Warren took to Twitter to offer a response.

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Within 24 hours, Warren had another tweet -- that took a decidedly different tack on Soleimani's killing. (Bolding is mine.) "Donald Trump ripped up an Iran nuclear deal that was working," tweeted Warren. "He's repeatedly escalated tensions. Now he'sa senior foreign military official. He's been marching toward war with Iran since his first days in office—but the American people won't stand for it."

Then, in a Sunday interview with CNN's Jake Tapper , Warren referred to Soleimani as only "a government official, a high-ranking military official" -- and suggested that Trump may have ordered the killing of the Iranian commander to distract from his pending impeachment trial in the Senate.

"Next week, the President of the United States could be facing an impeachment trial in the Senate," Warren told Tapper. "We know he's deeply upset about that. And I think people are reasonably asking, why this moment? Why does he pick now to take this highly inflammatory, highly dangerous action that moves us closer to war?"

Which, wow. We went from "murderer" to "wag the dog" in the space of a few days.

Which is mind-bending. And confusing -- until you realize the "why" behind Warren's rapid change of heart on Soleimani. Which is this: because the liberal left didn't like her initial statement and she needs those voters to have a chance at winning the Democratic presidential nomination this year.

Compare what Warren said upon the news of Soleimani's death with what fellow liberal -- and 2020 rival -- Sen. Bernie Sanders said. Sanders described the killing as as "assassination" from the start and added: "Trump's dangerous escalation brings us closer to another disastrous war in the Middle East that could cost countless lives and trillions more dollars. ... Trump promised to end endless wars, but this action puts us on the path to another one."

That comparison did not work to Warren's benefit -- particularly among the left on Twitter, where her initial statement was pilloried.

"'[Bogeyman] was a murderer... BUT" -> this is the formula used by useful idiots of warmongers," tweeted Ben Norton, a filmmaker and activist. "Warren is helping Trump sell a war of aggression on Iran with this ridiculous take."

And a slew of people on Twitter noted that Warren had voted for Trump's defense budget.

Given where she is in the race, Warren simply could not withstand that sort of criticism from the left. After a surge last summer -- fueled by liberals jumping to her from Sanders, Warren has watched that movement go the other way in recent months. In a CNN national poll released last month, she fell to 16% -- behind Sanders (20%) and former Vice President Joe Biden (26%). Among liberals, Warren (26%) and Sanders (25%) were in a statistical dead heat.

That finding is consistent with more recent data out of Iowa and New Hampshire that suggests Warren has now fallen behind Biden and Sanders (and, in Iowa, former South Bend Mayor Pete Buttigieg as well).

For Warren to be anywhere but in absolute lockstep with Sanders, then, on Soleimani's killing would have amounted to another data point for liberals (her sort-of walk-back from "Medicare for All" being another) that she was simply not a "real" liberal like the Vermont senator. So she changed her statement. And then changed again -- ending the week by not-so-subtly suggesting that Trump only ordered the killing of Soleimani to distract from his coming impeachment trial.

Which is a long way from where she started the week. A very long way.