Updated from 6 a.m. EDT
 
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Here are five things you must know for Thursday, March 23:

1. -- U.S. stock futures pointed to a slightly higher start for Wall Street on Thursday ahead of a crucial vote on health care reform in the U.S. and a speech by Federal Reserve Chair Janet Yellen in Washington. 

The passage of the Republicans' health care bill looks tenuous as a number of GOP lawmakers withhold their support ahead of the House vote on Thursday. Donald Trump has been pushing hard for House Republicans to vote for the bill, meeting with wavering lawmakers at the Capitol and the White House. Trump reportedly told lawmakers that their seats would be on the line in 2018 if they didn't back the bill.

The measure would repeal major parts of former President Barack Obama's health law, the Affordable Care Act, capping future funding for Medicaid and cutting tax increases for high-income families, health insurance companies and drugmakers. Speaker Paul Ryan's bill has been widely criticized on both sides of the aisle. The Congressional Budget Office calculated that 24 million more people will be uninsured by 2026 under the Republicans' bill, including 14 million more by 2018. Premiums are expected to jump 20% in the individual market in 2018 and 2019.

A failure to pass the bill would be a crushing blow for Trump so early in his presidency and investors may take it as a signal that he could find it increasingly difficult to push through his ambitious agenda of tax reform, regulatory change and fiscal stimulus.

Meanwhile, Yellen, a little more than a week after the Federal Reserve boosted interest rates, is scheduled to give the opening keynote address at the Federal Reserve System Community Development Research Conference in Washington at 8:45 a.m. EDT. Minneapolis Fed President Neel Kashkari, the only member of the Fed who didn't agree interest rates should be raised earlier this month, is scheduled to participate in a Q&A session at the conference at 12:30 p.m.

The economic calendar in the U.S. on Thursday also includes weekly Jobless Claims at 8:30 a.m., and New Home Sales for February at 10 a.m.

2. -- London Metropolitan Police said Thursday their investigation into the deadly terrorist attack Wednesday outside the Palace of Westminster in central London that left four people dead and 40 more injured would focus on the attacker's "motivation and preparation."  

In an official statement outside New Scotland Yard headquarters in London, acting Deputy Commissioner Mark Rowley said that six addresses around the country had been searched and that eight arrests were made (up from initial reports of seven), including during an overnight raid on a house in Birmingham.

"Greater clarity is now developing regarding the casualty figures as we have now collated information from the public and five hospitals -- the latest figures I have are that there are currently four dead and 29 people were treated in hospital," Rowley said. "We are still collating numbers of walking wounded and of those in hospital sadly seven of them are in a critical condition." 
 
U.K. Prime Minister Theresa May said the suspected Westminster attacker was British-born. May also confirmed Thursday that 40 were injured in the attack, including one American.
 
3. -- Apple ( AAPL - Get Report) finalized a deal on Wednesday to acquire Workflow, a tool that lets users hook together apps and functions within apps in strings of commands to automate tasks, according to a report from TechCrunch.
 
Financial terms of the deal weren't disclosed.

The app was made by a small team that includes Ari Weinstein, a former iPhone jailbreaker, TechCrunch reported.

Apple acquired the Workflow app, along with a team of Weinstein and others. In a somewhat uncommon move for Apple, the app will continue to be made available on the App Store and was made free on Wednesday, TechCrunch reported.

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4. -- Earnings are expected Thursday from  Accenture  ( ACN - Get Report) , KB Home  ( KBH - Get Report)  , GameStop ( GME - Get Report) and Micron Technology  ( MU - Get Report) .
 
5. --Jay Clayton, a well-connected Wall Street lawyer who is Donald Trump's pick to lead the Securities and Exchange Commission, is likely to face sharp questions from Democrats at his confirmation hearing Thursday over his years of work for Goldman Sachs ( GS - Get Report) and other financial giants.

Trump already has drawn upon Goldman alumni for key financial posts in his administration -- notably for Treasury secretary, Steven Mnuchin, and the head of the National Economic Council, Gary Cohn. Clayton, a partner in the white-shoe law firm Sullivan & Cromwell, has done significant legal work for Goldman, according to the Associated Press.

As SEC chairman, Clayton would be in charge of protecting investors from wrongdoing on Wall Street. He would oversee the enforcement of rules written by the SEC under the law that reshaped the regulation of banks and Wall Street after the 2008 financial crisis and the Great Recession. He also would take part in deciding on enforcement actions that SEC attorneys bring against corporations and financial firms.