Support for the Republican tax cut legislation signed into law late last year has steadily increased in recent weeks, but less than 40 percent of Americans approve of the bill, a poll released Wednesday showed.

A Gallup Poll, conducted from Feb. 26 through March 4, found 39 percent of voters approve of the tax bill. That’s a 6-point increase from January's numbers, and a 10-point increase from December when the law was signed, Gallup found.

Approval of the bill is split sharply along partisan lines. While 80 percent of Republicans and Republican-leaning independents approve of the law, just 11 percent of Democrats and Democratic-leaning independents support it.

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The law passed through Congress without a single Democratic vote. Democrats argued the bill overwhelmingly favored wealthy individuals and corporations.

Republicans argued the law would become more popular once voters saw an increase in their paycheck. Gallup found 32 percent of adults have seen an increase in their take-home pay because of the tax law so far.

However, Republican lawmakers have worried in recent days that President Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE's proposed tariffs on steel and aluminum could wipe away the economic gains of the tax law.

The tax bill has become a key issue for both parties as campaigns ramp up for this year's midterm elections. Trump, Vice President Pence and others have spoken at events around the country in recent weeks to tout the legislation's positive effects.

Democrats, meanwhile, have launched an ad campaign pitching the GOP bill as a "tax scam" that favors the wealthy.