Opponents of the legislative filibuster have made big gains this summer in their effort to abolish the Senate’s requirement for supermajorities to approve major legislation.

But any obituary of the filibuster might be premature, because recent history suggests Senate leaders will only pull the trigger on nixing the filibuster’s powers when there is a guaranteed big victory to follow. And it’s unclear when all the stars will align for such a major win.

The boldest proposals on the right — repealing the Affordable Care Act, creating private investment accounts instead of Social Security — failed to win simple majority support when Republicans controlled all the levers of power in Washington. And the most ambitious proposals among 2020 Democratic presidential aspirants, such as Medicare-for-all, remain well short of majority support in the House and Senate.

Several top Democratic contenders have pledged to at least consider leading the effort to abolish the filibuster, and former Senate majority leader Harry M. Reid (D-Nev.) joined the cause in an op-ed calling for its end.

“If the Senate cannot address the most important issues of our time, then it is time for the chamber itself to change,” Reid wrote in the New York Times.

That echoes the themes advanced by the most strident opponents of the filibuster, who are afraid that if Democrats win the White House and the Senate in the 2020 elections Majority Leader Mitch McConnell (R-Ky.), who would then become minority leader, would still stymie their aggressive agenda with filibusters.

“When Democrats next have power, we should be bold,” Sen. Elizabeth Warren (D-Mass.) said in April at the Rev. Al Sharpton’s National Action Network gathering. Predicting that McConnell would revert to his behavior during the Obama administration, Warren added, “Then we should get rid of the filibuster.”

With little fallout from nuclear option, Senate’s legislative filibuster is in jeopardy

Every majority leader of the last 15 years began his reign praising tradition and touting the Senate’s role as the cooling saucer to the House’s more partisan impulses, but eventually tried to rip apart the rules protecting minority rights to filibuster.

Each of those majority leaders — Bill Frist (R-Tenn.), Reid and McConnell — eventually reached a point where they saw a big victory in front of them if they could only have a 51-vote threshold. Frist wanted to break a blockade of Democratic filibusters of George W. Bush’s circuit court nominees, a battle that ended with a negotiated compromise among centrists in May 2005.

By 2013, with Republicans filibustering Barack Obama’s nominees to the U.S. Circuit Court of Appeals for the District of Columbia, Reid initiated the “nuclear option” to lower the threshold to ending debate to just 51 votes on all nominees except those to the Supreme Court. Democrats have now appointed a majority of judges on what is considered the second most important federal bench.

And in 2017, faced with a blockade of Neil M. Gorsuch, McConnell rounded up GOP support for eradicating filibuster rights on Supreme Court nominees, clearing the way for Gorsuch and then Brett M. Kavanaugh to win confirmation on narrow, almost party-line votes.

Those moves left the 60-vote filibuster in place for legislation only, what traditionalists in both parties say is the last thing preventing the Senate from just turning into the more partisan-driven House.

Many conservatives, including Trump, pushed McConnell to eliminate the legislative filibuster when Republicans held the majority in both chambers. But, as the 2017 effort to repeal the ACA demonstrated, Republicans did not have 51 votes to pass that legislation under special budget rules, so it became a moot point.

With Democrats now controlling the House, McConnell faces no pressure to eliminate the legislative filibuster. As long as Congress is split, only legislation with broad bipartisan support can pass the House and Senate, making the filibuster pointless.

House Republicans, dealing with a rash of retirements, are not behaving like a group expecting to win back the majority anytime soon.

So that makes Democrats the only party seriously considering going “nuclear” on the legislative filibuster. Senate Minority Leader Charles E. Schumer (D-N.Y.) has been coy about his intentions should Democrats win a clean sweep in 2020, but the pressure will be enormous to end the filibuster.

The question will be, for what legislation?

Proponents of stricter gun control face a reality check in the Senate

Warren supports the Medicare-for-all proposal from Sen. Bernie Sanders (I-Vt.), but aside from those two high-profile candidates for president, there are just 12 other co-sponsors for the legislation. And worrying about the Senate whip count presumes the legislation would pass in the House. It probably wouldn’t.

Rep. Pramila Jayapal (D-Wash.), the House sponsor of Medicare-for-all, has 117 co-sponsors, a bare majority of the Democratic caucus but still 100 votes shy of the minimum needed for passage.

The House and Senate resolutions calling for a “Green New Deal” to combat climate change have 95 and 13 supporters, respectively. Some Senate Democrats are quietly discussing the use of special budget rules to approve portions of climate legislation, such as a tax on carbon, on a simple-majority basis that would not require blowing up the legislative filibuster.

House Democrats, as of now, also are short of the 218 votes needed to pass an assault weapons ban.

The most likely issue that could push Schumer into a nuclear war might be immigration. Back in 2013, a bipartisan majority of 68 senators, including 14 Republicans, supported legislation giving a path to citizenship for about 11 million undocumented immigrants if they spent 10 years meeting a set of requirements.

But only four or five Republicans who supported that bill will be in the Senate in two years, and if Republicans filibustered an immigration bill, Schumer might be left with no other choice but to void that option.

Of course, the biggest thing the filibuster has going for it is divided government. Democrats need a net gain of three seats to get to a 50-50 Senate, in which case the presidential winner would take the majority based on the vice president casting the tie-breaking vote.

That’s possible based on the seats currently in play, but there’s one ironic possibility: Warren, the biggest advocate for eliminating the filibuster, would resign from the Senate in January 2021 if she were to win the presidency, and a 50-50 Senate would disappear.

Massachusetts Gov. Charlie Baker (R) would immediately appoint a Republican to replace her. Under state law, a special election would be held about five months later.

That would leave McConnell as majority leader for President Warren’s first 100 days and possibly beyond, depending on that special election.

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