Attorney General William Barr is scheduled to travel down Pennsylvania Avenue on Tuesday to make what could be a very difficult sales pitch to Senate Republicans.
Provisions in the Foreign Intelligence Surveillance Act are set to expire next month, and Barr is expected to try to persuade senators to vote to reauthorize them.
Criticism of FISA is now mainstream among many Republicans and some Democrats after a thorny subplot from the Russia investigation.
This isn't the first time establishment figures have tried to sell members of Congress on supporting it over their own political instincts, but the circumstances that led Barr to this visit may mean now is the toughest time in years to try to convince lawmakers.
One silver lining for the attorney general on his errand is that he at least has support from Senate Majority Leader Mitch McConnell, R-Ky. The leader invited Barr to have lunch with the Republican conference weeks ago, according to one source familiar with the planning.
"Reauthorization of these certain programs is a priority for both Leader McConnell and AG Barr," the source said.
FISA is the legislation that permits national security officials to collect Americans' communications.
Congress first structured the authorities after President Richard Nixon's abuses and then expanded them after the 2001 terrorism attacks — and some of those newer authorities have proved controversial ever since.
One way in which members of Congress were able to compromise on expanded surveillance authority was by including time limits, forcing themselves or their successors to reevaluate whether to preserve the powers they authorized.
Parts of FISA are set to expire in mid-March, unless Congress votes to revive them and then President Trump agrees by signing the legislation.
The provisions' original sunset date was in December, but members of Congress agreed on an extension establishing the new deadline.
Deputy Assistant FBI Director Michael Orlando appeared before the Senate Judiciary Committee in November to advocate for the reauthorization; here's how he detailed the aspects of the law in question and said why the bureau considered them so important.
What's controversial about the legislation?
FISA always has had its skeptics.
Civil libertarians in both parties worried about giving the government too much power to conduct surveillance. And more recently, the Russia investigation has amplified the worries of those who argued that what they call unscrupulous investigators can too easily exploit a permissive law and violate some Americans' rights.
Justice Department Inspector General Michael Horowitz concluded that some FBI and Justice Department officials did exactly that in the case of a former campaign aide of Trump's, Carter Page.
The bureau and the department also were rebuked by the secret court that oversees surveillance cases in a black eye for federal law enforcement that followed months of scourging by Trump's allies in the Russia imbroglio.
The Russia investigation was opened and conducted mostly properly, the investigation found, and its conclusions weren't questioned. But what the Page subplot exposed, critics said, was that the kind of FISA abuse that earlier may have been believed only theoretical had, in fact, actually happened.
"If the American people hear this, and they say 'this can happen against a campaign, for the presidency of the United States' — what happens in an ordinary FISA case?" asked Sen. Ben Sasse, R-Neb., in a Senate hearing about the Page investigation.
Barr and FBI Director Christopher Wray have vowed to change investigators' practices to prevent incorrect or incomplete information from reaching a FISA judge as it did in the Page case.
But the lingering controversy over the law, combined with the Page example — and following months of charges about "spying" on Trump's campaign and what critics call bias in federal law enforcement against Trump — may have imperiled sufficient support among Republicans to reauthorize the sections that are due early next month.
Barr's goal is to try to change enough minds among the Senate's Republicans, who control the majority in the chamber.
What about Trump?
As the attorney general prepares to visit the Capitol, it isn't immediately clear what kind of support exists for FISA there, and it also isn't clear what Trump is prepared to sign.
Trump signed legislation extending different aspects of FISA in 2018 after an earlier flap about whether aides of then-candidate Trump might have been swept up in American surveillance of foreigners during the election.
Trump said at the time he was willing to permit the authority to continue because of the case made by the intelligence establishment, led by then-Director of National Intelligence Dan Coats, about the value it afforded to national security.
Today the DNI post is vacant, and although Trump has said he's choosing between a group of four nominees, there is no one to make the same kind of concerted sales pitch that Coats and his colleagues have in the past.
Barr appears to be taking on that burden.
Moreover, Trump has widened and deepened his attacks on the intelligence establishment and the "dirty cops" he has criticized within the FBI. "FISA" has become synonymous with overreach and abuse of power for the president and supporters.
Trump, meanwhile, was unmoved by Barr's pleas for him to keep silent about Justice Department business. So the attorney general must not only try to bring along skeptical Senate Republicans about reauthorizing the surveillance legislation; he may also need to convince his own boss.