In December 2007, then-Senator Barack Obama joined then-Senator Chris Dodd in threatening to filibuster the Foreign Intelligence Surveillance Act (Fisa). Senator Obama opposed provisions granting retroactive immunity to telecommunications companies that shared private client information with the government. His office released a statement:

"Granting such immunity undermines the constitutional protections Americans trust the Congress to protect. Senator Obama supports a filibuster of this bill …"

Senator Obama was right. Had I been in the Senate, I would've voted with him. I've even filibustered myself over civil liberties issues I believe are important.

Later, supporting an amendment that he believed repealed retroactive immunity from Fisa, Senator Obama said in February 2008:

"We can give our intelligence and law enforcement community the powers they need to track down and take out terrorists without undermining our commitment to the rule of law, or our basic rights and liberties."

Senator Obama in 2007 was rightly concerned that telecommunications companies might get away with sharing clients' private information without legal scrutiny. This week, we learned that the president's National Security Agency compelled Verizon to hand over all of its client data records.

Senator Obama in 2008 wanted to track potential terrorist activity "without undermining our commitment to the rule of law, or our basic rights and liberties". Today, President Obama undermines the rule of law, basic rights and core liberties – all in the name of tracking terrorists.

There is always a balance between security and liberty and the American tradition has long been to err on the side of liberty. America's founders feared a government powerful enough to commit unreasonable searches and seizures and crafted a constitution designed to protect citizens' privacy.

Under this administration, the Internal Revenue Service (IRS) has targeted political dissidents, the Department of Justice has seized reporters' phone records, and now we've learned the NSA seized an unlimited amount of Verizon's client data. Just when you think it can't get any worse under this president, it does. This is an all-out assault on the constitution. These actions are unacceptable under any president, Democrat or Republican.

I can remember well a Senator Obama who joined the Democratic chorus against the warrantless wiretapping of the Bush administration. Now, that chorus has gone mute. The Guardian's Glenn Greenwald has noted what he sees as "a defining attribute of the Obama legacy: the transformation of what was until recently a symbol of rightwing radicalism – warrantless eavesdropping – into meekly accepted bipartisan consensus."

Not every Republican or Democrat is part of that consensus. When the Senate rushed through a last-minute extension of the Fisa Amendments Act over the holidays late last year, Senator Mike Lee (Republican, Utah) and I offered an amendment requiring stronger protections on business records that would've prohibited precisely the kind of data-mining the Verizon case has revealed. Senator Ron Wyden (Democrat, Oregon) introduced an amendment to require estimates from intelligence agencies of how many Americans were being surveilled. Both these measures were voted down.

Just last month, I introduced the Fourth Amendment Preservation and Protection Act, which if enacted would've protected Americans from exactly the kind of abuses we've seen recently. It was also voted down.

On Thursday, I announced my Fourth Amendment Restoration Act of 2013, which ensures that no government agency can search the phone records of Americans without a warrant based on probable cause. We shall see how many join me in supporting a part of the Bill of Rights that everyone in Congress already took an oath to uphold.

If the president and Congress would simply obey the fourth amendment, this new shocking revelation that the government is now spying on citizens' phone data en masse would never have happened. That I have to keep reintroducing the fourth amendment – and that a majority of senators keep voting against it – is a good reflection of the arrogance that dominates Washington.

During my filibuster, I quoted Glenn Greenwald, who wrote:

"There is a theoretical framework being built that posits that the US government has unlimited power. When it comes to any kind of threats it perceives, it makes the judgment to take whatever action against them that it warrants without any constraints or limitations of any kind."

If the seizure and surveillance of Americans' phone records – across the board and with little to no discrimination – is now considered a legitimate security precaution, there is literally no protection of any kind guaranteed anymore to American citizens. In their actions, more outrageous and numerous by the day, this administration continues to treat the US constitution as a dead letter.

Senator Obama said of President Bush and Fisa in 2008:

"We must reaffirm that no one in this country is above the law."

No one in America should be above the law. Including this president.