The US House of Representatives has taken the first step toward demolishing President Barack Obama's signature healthcare law, known as Obamacare. Republicans passed a budget measure to introduce a bill – which Democrats cannot block – to roll back the law. But members of both parties in Congress are concerned about a lack of replacement for Obamacare. <br/><br/> The political showdown raises a big question mark over medical coverage for more than 20 million Americans. The measure passed in the House nearly on a party-line vote, 227-198, delivering a blow to President Obama's legacy a week before he leaves office.<br/><br/>It instructs four committees on Capitol Hill to draft repeal legislation by 27 January. The Senate passed the resolution by 51-48 on Thursday.