Since the Senate is evenly split 50/50 between Republicans and Democrats (the Vice-President can cast tie-breaker votes), the Democrats would need ten Republican senators to pass their legislation, and given the radical nature of much of that agenda ten GOP votes are going to be very hard to come by.
Thus, the talk about quashing the filibuster so that they can pass bills with a simple majority (all 50 Democrats plus the Vice-President).
But what would happen if the Democrats eliminated the filibuster. Senate Minority Leader Mitch McConnell promised a "scorched earth" Senate, the Senate would look like “100-car pileup—nothing moving,” but what does that mean? Kimberly Strassel at the Wall Street Journal (paywall) provides the details for us:
...there are 44 standing rules of the Senate; the filibuster is but one....To the extent the Senate functions at all ... it is only because senators willingly relinquish those prerogatives. Mr. McConnell on Tuesday described a world in which they don’t, which he called a “scorched-earth Senate.”The irony here is that the Democrats anticipate that by eliminating the filibuster the Biden agenda could more easily pass through the Senate, but if they do abrogate the filibuster rule the result would be that nothing would get through the Senate.
It’s a world without “unanimous consent,” in which a senator asks all 99 colleagues to give up their right to object to a proposal. Senate leaders rely on unanimous consent dozens of a times a day. You need consent to open the Senate before noon, to dispense with the reading of the preceding day’s journal, to move to business, to avoid reading out loud the text of every amendment and resolution, to avoid roll call votes. The Senate functions because most consent requests are granted.
When they aren’t? It takes only one Republican to object to a request but a majority to overcome most objections. Mr. Schumer [The Democratic Leader in the Senate] might at any time need all 50 of his members—and the vice president—on the floor to move things along. Likewise to override a flow of “points of order.” All day, every day.
Republicans could flit in and out, and it would only take a handful of members to force roll calls for all these votes, eating up more hours. Democratic senators and Kamala Harris would essentially live at the Capitol, constantly on call. If even one was absent at a crucial moment, the Senate would essentially shut down.
Now add in “quorum” calls. Any senator can question, pretty much any time, whether the Senate truly has 51 senators on the floor (the vice president doesn’t count). It’s unclear whether a lone Republican could issue a quorum call, flee and stymie Senate business until the sergeant of arms rounded him back up. But even if that lone Republican stayed, quorum calls would eat up hours. The Senate secretary is required in each case to call the roll, of all 100 senators.
Anyone who has ever watched C-Span 2 knows this takes ages.
There are even more creative ideas, but these tools alone would be enough to paralyze the institution. The Senate convenes. Quorum call. The presiding officer asks for consent to forgo reading yesterday’s journal. Republicans object. Roll call vote. The officer asks for consent to speed through “morning business.” Republicans object. Democrats move to get on an issue. Point of order. Roll-call vote. Quorum call. Republicans object to the motion. Roll-call vote. A speech. Quorum call. Etc., and so on, until adjournment.
The Democrats seem to have failed to learn a lesson they should've learned over a decade ago. Back then they were in the majority and were trying to get President Obama's left-wing federal judges confirmed, but the Republicans were loath to seat radical judges and used the filibuster rule, which back then applied not only to legislation but also to approving federal judges and Supreme Court Justices, to block their appointments.
The Senate Majority Leader at the time, Harry Reid, decided that, very well, he would eliminate the Senate filibuster as it applied to federal judges, and they were thus able to get Obama's appointees through.
At the time Senator McConnell warned that toying with the filibuster would someday come back to haunt the Democrats, and it did. When Donald Trump became president he had the opportunity to appoint several Supreme Court Justices.
The Republicans were now in the majority in the Senate so the Democrats planned to block Trump's appointments with the filibuster which still applied to Supreme Court nominees, but McConnell said that since the Democrats had removed the filibuster for federal judgeships there was no logical reason for keeping it in place for Supreme Court nominees, so he eliminated the rule for SCOTUS justices, and as a result Trump was able to get three conservative justices confirmed to the Supreme Court on simple majority votes.
Moreover, since the Democrats had already removed the filibuster as a barrier to federal judgeships, President Trump was also able to appoint a record number of conservative judges to the federal bench with simple majorities in the Senate.
If the Democrats continue to manipulate the Senate rules by eliminating the legislative filibuster, assuming that they have the votes to do it, they will once again rue their short-sightedness, and McConnell will once again see to it that they do.