Republican Donald Trump and Democrat Hillary Clinton are in a statistical tie in the latest Reuters/Ipsos poll released on Wednesday, showing a tight battle for the White House as the two likely nominees turn their attention to the Nov. 8 election.

The narrowing poll numbers are the result of both a gain by Trump and a drop by Clinton in the days since the New York real estate mogul effectively secured the Republican nomination when his two remaining rivals quit last week.

The national poll found 41 percent of likely voters supporting Clinton and 40 percent backing Trump, with 19 percent undecided. The online survey of 1,289 people was conducted over five days in the last week and has a credibility interval of 3 percentage points.

While the general election campaign has hardly begun, the poll marks a shift from a similar Reuters/Ipsos survey conducted over the five days before Trump effectively became the nominee. That poll showed Clinton at 48 percent and Trump at 35 percent.

The former US secretary of state's loss in the Democratic primary election to Bernie Sanders in West Virginia on Tuesday signaled possible trouble for her in industrial states in November.

Trump has taunted Clinton in recent days, saying she "can't close the deal" against primary opponent Sanders, a U.S. senator from Vermont.

But Trump still does not have some senior Republicans on board for his own campaign after primary election battles in which he promised to build a wall on the Mexican border to halt illegal immigration, and temporarily ban Muslims from entering the United States.

Several Republican leaders -- including House of Representatives Speaker Paul Ryan -- are withholding their support from Trump.

The former reality TV star will face pressure to tone down his rhetoric and clarify his policy positions when he visits Republican lawmakers on Thursday.

Trump On Tax

Trump's campaign has largely lacked policy specifics and he has often said the positions he has staked out are merely opening salvos for future negotiations with both Democrats and Republicans.

But he may be considering an overhaul of his tax proposal, a move that could bring down the price tag and keep it in line with conservative ideologies.

His tax plan, which carries a $10 trillion sticker price, has been under scrutiny as he has worked to tone down remarks about raising taxes on wealthy Americans, saying the rich might simply get a smaller tax cut than he originally proposed.

A possible rework of the plan has been led by conservative economists Larry Kudlow, who hosts a program on CNBC, and Stephen Moore, who works with the conservative think tank Heritage Foundation.

"I have worked a little bit with Larry Kudlow to help try to tweak the plan to try to just... provide the maximum amount of economic juice and to reduce the cost," Moore told Reuters. "What we were working with the campaign a little bit on is how can we get that cost down, cut it by half or more, without disrupting the main growth elements of the plan."

Trump's attention to tax is another sign that the economy will play a major part in the election.

For Clinton, 68, her failure to win over voters deeply skeptical about the economy underscored how she still needs to court working-class voters in the Rust Belt, including key states such as Ohio and Pennsylvania. West Virginia has one of the highest unemployment rates in country.

Sanders, who has vowed to take his campaign all the way to the Democrats' July convention in Philadelphia, has repeatedly said he is the stronger candidate to beat Trump in November, and following his West Virginia win, he emphasized economic themes.

In West Virginia, roughly six in 10 voters said they were very worried about the direction of the U.S. economy in the next few years, according to a preliminary ABC News exit poll. The same proportion cited the economy and jobs as the most important issue.