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On Tuesday, representatives from Facebook (FB), Amazon (AMZN), Apple (AAPL) and Google (GOOG) are set to testify at a House hearing on “online platforms and market power,” in what could be the industry’s most high-profile grilling session since tech antitrust scrutiny ramped up in Washington a month ago.

Just a few hours before that, David Marcus, a top Facebook executive is scheduled to appear in a different hearing before the Senate Banking Committee. This hearing will focus on the company’s recent proposal for a new digital currency called Libra, a plan that Sen. Sherrod Brown, a Democrat and ranking member on the committee, said raises more “anti-competitive concerns.”

The dramatic day on Capitol Hill highlights the harsh spotlight politicians on both sides of the aisle now place on the country’s largest tech companies. Once viewed in purely glowing terms as icons of American innovation, these businesses now face a “top-to-bottom” antitrust probe from the House Judiciary Committee and two federal agencies paving the way for potential investigations into their market dominance.

And yet, the Libra hearing is also a reminder that these tech firms are continuing to invest aggressively to expand their businesses, despite mounting concerns that they are already too big and powerful.

In the weeks since news of the potential US antitrust probes first broke, Google announced a $2.6 billion acquisition to bolster its cloud computing division, Jeff Bezos teased plans for Amazon to spend billions to launch thousands of satellites that provide broadband internet, and Facebook unveiled Libra with the potential to change financial and payment systems around the world.

On the one hand, these continued investments are necessary to appease investors by showing new avenues for growth. But these announcements may only add to the sense that the giants of Silicon Valley are unconstrained and growing more powerful by the day.

“The optics definitely aren’t great, but I’m not sure they have much of a choice,” said Bradley Tusk, a regulatory adviser who has worked with a number of tech companies, including Uber (UBER) and Tesla (TSLA). “The markets demand that they keep advancing and, at their stage, only major new products or acquisitions can move the needle.”

Tusk continued: “It will give Congress even more ammunition to use in the hearings, so the pressure on the reps from each company to perform well is even higher.”

Even before Congress launched its antitrust probe, there were growing calls to check the tech industry’s power. In early May, Facebook cofounder Chris Hughes called for the company to be broken up. Democratic presidential candidate Sen. Elizabeth Warren put out an aggressive plan in March to break up Facebook, Google and Amazon, leading other presidential hopefuls to echo concerns about these companies.

These calls followed a broader shift in sentiment about the tech industry. Since the 2016 election, internet giants like Facebook and Google have been embroiled in a series of PR crises over data privacy, the role their platforms played in election meddling, and the spread of misinformation, raising concerns about the full impact these powerful businesses are having on society. At the same time, these internet companies have increasingly expanded beyond their original markets into new categories, including healthcare, entertainment and transportation.

As more politicians in DC have begun to focus on Silicon Valley’s concentration of power, the tech companies have trotted out multiple lines of defense in what could be a preview of the talking points at the upcoming hearing. Representatives for Facebook and Amazon did not respond to a request for comment on this story. A Google spokesperson directed CNN Business to the company’s previous remarks on antitrust concerns.

Google CEO Sundar Pichai told CNN Business last month that being bigger “does offer many benefits,” including the ability to invest in cutting edge technologies such as artificial intelligence and quantum computing. Similarly, Facebook CEO Mark Zuckerberg recently said being bigger makes it possible for the company to invest in preventing the spread of misinformation and election interference. Execs from both companies have also suggested that breaking up US tech companies could benefit businesses in other countries, namely China.

Representatives from Facebook will testify in multiple hearings on Capitol Hill next week. The hearings underscore the greater antitrust scrutiny directed at Facebook and its peers, and the industry's unwillingness to pause its big bets in the face of that scrutiny.

Another popular approach is for executives to define their relevant market as broadly as possible in order to make themselves seem smaller, a clear attempt to undercut the foundation of any antitrust argument. Amazon may be a dominant force in the US ecommerce market — accounting for nearly 50% of it in 2018, by one estimate — but the company has repeatedly stressed to the media that it represents less than 1% of the global retail market. Likewise, Facebook and Google may dominate US digital ad spending so much that they’re often referred to as a “duopoly,” but Zuckerberg wants you to know that Facebook makes up less than 10% of the global online advertising market.

The tech companies could adopt a similar line of defense if questioned on their more recent investments. After Google agreed to acquire business intelligence platform Looker for $2.6 billion last month, the company’s new cloud computing head told one publication the deal should not be an antitrust issue because a number of similar services remain on the market. Perhaps more to the point: while Google is the undisputed leader in search, it is behind Amazon and Microsoft in cloud computing.

For now, slowing or stalling their big bets out of fear of pending regulation and looming antitrust probes — and ceding ground to new and existing rivals in the process — almost certainly poses a greater risk to the tech companies than any potential regulatory backlash to this continued investment.

Case in point: Bill Gates recently admitted that his biggest mistake running Microsoft was failing to build a mobile operating system to rival Apple’s. If it had, Microsoft might have avoided its high-profile stumbles in the smartphone market. “We were distracted during our antitrust trial,” he said at an event last month. “We didn’t assign the best people to do the work.” Other tech companies can’t risk making that same mistake.

“Critics don’t like the big tech companies because of the size they have already obtained and the power they are perceived to have over speech, politics and privacy,” said Doug Melamed, former acting assistant attorney general at the Justice Department in charge of the antitrust division. “The companies pulling their punches now is not going to change that.”

The tech companies, Melamed says, “no doubt believe, correctly in my view, that there is no way the populists will get legislation this term to break up the companies or anything like that.”