Senator Bernie Sanders, who has promised to do "whatever it takes" to block the deal President Obama cut to extend tax breaks for billionaires and create a sweeping estate-tax exemption for millionaires, began to wage what he said could be called a "filibuster" on the floor of the Senate Friday.

After Sanders took the rostrum at 10:24 a.m. Friday, the Vermont Independent posted a message on his his twitter account that read: "You can call what I am doing today whatever you want, you [can] call it a filibuster, you can call it a very long speech…"

Sanders spoke for more than eight hours. His bold gesture grabbed the attention of the nation, as Senate video servers were overwhelmed when more than 12,000 people tried to watch the speech online.

For all the excitement, Sanders was not actually blocking a vote on the tax deal. The Senate will not take the issue up until Monday, at the earliest.

Sanders was, however, sending a powerful signal about the fight to come.

The senator concluded his remarkable 8.5 speech with a call to action. "If the American people stand up and say, ‘we can do better than this, that we don’t need to drive up the national debt by giving tax breaks to millionaires and billionaires,’ (if) the American people are prepared to stand – and we’re prepared to follow them – I think we can defeat this proposal," he declared. "I think we can come up with a better proposal which better reflects the needs of the middle class and working families of our country and, to me, most importantly, the children of our country.  And with that, Madam President, I would yield the floor."

The senator was not alone in his sentiment. He was supported on the floor by an old progressive ally, Ohio Senator Sherrod Brown, and by a moderate Democrat, Louisiana’s Mary Landrieu, who does not always make common cause with the democratic socialist senator from Vermont.

Landrieu referred to the agreement the White House is trying to force the congress to accept as "almost morally corrupt."

For the most part, however, Sanders held the podium Friday, speaking calmly and in great detail about his specific objections to the tax-cut deal and about his broader concerns about federal policies that favor the wealthiest Americans while neglecting working families.

Sanders’s speech capped a week in which Democrats in the House and Senate raised became increasingly vocal in their opposition to the deal that President Obama initially advanced as a take-it-or-leave-it proposition.

First House Democrats rejected the tax deal President Obama cut with Senate Democrats and told Speaker Pelosi to negotiate a better agreement.

Then, on Friday, eight Senate Democrats told Majority Leader Harry Reid that they want to amend the deal to cap tax breaks for the rich and protect Social Security. 

In a letter circulated by Oregon Senator Jeff Merkley and Louisiana Senator Mary Landrieu, the senators said: "We have grave misgivings about the recent tax agreement.  We hope that the Senate can improve on it.  We look forward to working with you to ensure a vote on our amendment to strengthen Social Security in lieu of bonus tax cuts for people who are doing quite well."

They also offered an outline for a plan that would to restore tax rates on income over $1 million per year to the Clinton-era rates, and to dedicate the resulting revenues to shoring up the Social Security trust fund.

The White House will push back against any amendment strategy, fearing that changes might endanger Republican support for the agreement.

But the letter gives Reid a bargaining chip. He has a numbers problem. In addition to the eight signers of the letter—Merkley, Landrieu. Alaska’s Mark Begich, Hawaii’s Daniel Akaka, Ohio’s Sherrod Brown, Minnesota’s Al Franken, Colorado’s Mark Udall and California’s Barbara Boxer—several other members of the Senate Democratic Caucus have voiced strong objections to the agreement.

Sanders continues to talk of using a filibuster strategy to block the proposal. And her Vermont colleague, Patrick Leahy, has been bluntly critical.

So Reid can, and should, suggest to the White House that they really ought to talk to congressional Democrats about reworking the deal. At the very least, that strengthens Pelosi’s hand—especially as she raises concerns about the estate-tax exemption that has raised many objections on Capitol Hill. 

In those negotiations, however, Reid and Pelosi should also focus on the concerns about Social Security raised in the letter from the senators, whose worries need to be addressed. 

Here’s the letter to Reid: 

"The tax package announced by President Obama and Congressional Republicans includes some important provisions that we strongly support, but also a deeply misguided allocation of resources at a time that the United States does not have resources to waste. 

"The Senate, however, can make it better.  We ask that you ensure an opportunity for the Senate to vote on an amendment that will give the American people a clear choice whether they would prefer to give bonus tax cuts to the very wealthiest among us, as the package currently proposes, or to use these resources to strengthen Social Security.

"Success in America should rightly be celebrated, but the very wealthy do not need bonus tax cuts and America cannot afford to give them.  As you know, the agreement would require American taxpayers to borrow over $50 billion in order to give, on average, $100,000 in additional annual tax cuts to people earning over $1 million per year.  These bonus tax cuts are on top of the $43,000 per year that millionaires will receive in tax cuts on their first million dollars of income.  The Congressional Budget Office ranked these tax cuts dead last in terms of effectiveness in boosting economic growth and job creation.  In a time of urgent national needs and long-term deficits, we believe the country has higher priorities than these huge tax cuts for the very wealthy. 

"Specifically, we propose to amend the package to restore tax rates on income over $1 million per year to the Clinton-era rates, and to dedicate the resulting revenues to shoring up the Social Security trust fund.  The President’s National Commission on Fiscal Responsibility and Reform noted that in 2037, Social Security will exhaust its trust fund and be unable to pay full benefits, and consequently proposed a number of benefit cuts for seniors.  Improving Social Security’s finances is, in our opinion, a more important national priority than directing tens of billions of dollars in taxpayer money to a relative handful of families. 

"We have grave misgivings about the recent tax agreement.  We hope that the Senate can improve on it.  We look forward to working with you to ensure a vote on our amendment to strengthen Social Security in lieu of bonus tax cuts for people who are doing quite well."