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Feature, BBC North America Correspondent
Reporting from Washington, DC
On election night, Donald Trump repeated: "Promises made, promises kept."
Now that the Republicans have officially taken control of Congress, his "promises" are much easier to keep.
In Washington political parlance, it's called the "ruling triumvirate," when the president's party controls both houses of Congress - the House of Representatives and the Senate.
That control is what Donald Trump's Republican Party now possesses.
Complete control by one party was once common, but in recent decades it has become increasingly rare and lasted for shorter periods of time.
The party in power often loses parliamentary seats when the mid-term congressional elections are held two years later.
Both Trump and Biden enjoyed a "ruling trio" during their first two years in the White House, and both have learned that when you have that kind of control, it's no guarantee that it will always be the president's way.
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During his first two years in office, Trump passed a famous tax bill, cutting the corporate tax rate from 35 percent to 21 percent and cutting individual taxes.
But with some members of his own party resisting his surprise rise to the top in 2016, he has had trouble achieving other goals.
His plan to repeal the Affordable Care Act (known as Obamacare) failed when Senator John McCain of his own party refused to vote for it.
He didn't even manage to pass the bill on infrastructure as he promised.
During his first two years, when Democrats controlled the House and Senate, Biden managed to pass the American Rescue Plan, the Investments and Jobs Act, and the CHIPS and Science Act.
But he too had to make significant cuts to the spending and investment plans - called the Build Better Again package - after opposition from one of his own senators.
A major obstacle to full control by either party is that Senate bills require a three-fifths majority, or 60 votes, to bypass the filibuster, which allows senators to delay a vote on a bill while keeping debate open.
This means that when a party has a simple majority in the Senate, it will have to turn to rivals across party lines to get the bill passed.
Even with a healthy majority in the Senate this time, Trump will not have the magic 60 parliamentary seats that allow him to bypass all attempts by the opposition to delay the passage of the law.
And on Wednesday, Senate Republicans chose John Thune as their majority leader over Rick Scott of Florida, the clear favorite in the Trump camp, in a sign that some lawmakers want to regain independence (Trump has not officially endorsed Scott).
Despite all that, the "troika", if managed skillfully, really opens the door to possibilities for major legislative initiatives.
Trump's lead could be key to delivering on his big promises, such as the largest deportation of migrants in history; comprehensive, comprehensive tariffs on foreign imports; and abolition of environmental protection.
Using legislation to achieve these goals will make overturning these plans in the courts much more difficult, which Donald Trump was mired in during his first term when he made extensive use of executive orders that were regularly and often successfully challenged.
The judicial landscape has also shifted in Trump's favor.
A key success of his first term was the appointment of three conservatives to the Supreme Court, cementing a two-thirds majority for perhaps decades.
He also appointed more than forty judges to the federal appeals courts, turning several judicial districts into more conservative environments.
The Republican majority in the Senate also provides another key advantage.
Trump will be able to more easily get approvals for his own candidates for administrative positions, something he struggled with in 2017 when internal opposition to him in the Republican Party was still a significant factor.
All of this points to a busy and possibly tumultuous two years ahead, and as recent history shows, these "threes" don't last very long, so the incoming administration will want to accelerate.
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