"If we don't negotiate something fair, then we have tremendous retribution, which we don't want to use, but we have tremendous powers", Trump said on Wednesday during a cabinet meeting at the White House.
Vestager's other major scalps include Amazon and Apple.
The Commission has ordered Google to give manufacturers more freedom when deciding which apps to install on Android smartphones.
What is the case against Google?
The Commission, however, said that as Google obtains the vast majority of its revenues via its flagship product, the Google search engine, the company understood early on that the shift from desktop PCs to mobile Internet, which started in mid-2000, would be a fundamental change for Google Search.
"Most users are already completely hooked on Google services". Small or non-partners have no space in the web world dominated by Google.
Google's chief executive Sundar Pichai has blogged in response. Google maintains less transparency in its dealings with advt. buyers or publishers.
The European Commission alleges that by forcing device-makers to install Google apps on Android devices it gains a significant advantage over competitors. She said that European Union antitrust laws put a "special responsibility" on dominant businesses, meaning they can not deny other companies the chance "to compete with them on merit".
It delivers over 95 percent of apps downloaded to Android phones, European Commissioner Margrethe Vestager said, announcing the decision.
The 4.34 billion euro penalty comes on top of a 2.42 billion euro fine ($2.8 billion) that regulators imposed on Google a year ago for favoring its shopping listings in search results.
That figure represented a doubling in global revenue in only four years. The company faces daily fines of 5% of revenue if it doesn't obey.
Google immediately said it will appeal the ruling, arguing that its free operating system has led to lower-price phones and created competition with its chief rival, Apple.
Trump has lashed out at the EU - defending Google and saying he was right over European agendas. "They could these users to try their own services before they get completely hooked on Google". "If they do, advertisers will be drawn to those platforms, too, because the ROIs (return on investment) are very hard to replicate anywhere else", said Polar Capital fund manager Ben Rogoff.
"There is a significant danger of unintended consequences that penalizes the consumer". However, this is not the first time that Google is facing such a hefty penalty.
Still, some USA politicians welcomed the fine.