Sen. Chris Van Hollen, D-Md., predicted this week the new Republican tax cuts taking effect this year will take far too long to get to people, and that they therefore won't help Republicans in the 2018 midterm elections.

"It's called trickle-down [economics] for a reason," Van Hollen told the Washington Examiner.

"By the time the tax breaks actually start making their way to workers, they're very small. ... Millions of people are actually seeing increases," he added, referring to many in his home state.

Republicans have been gloating that not a single Democrat voted for the tax cut legislation, and therefore they get to claim none of the credit after companies around the country announce raises and bonuses. Van Hollen is arguing that 10 months is too short a time to see those benefits, speaking just before President Trump's Treasury Department rolled out new withholding tables to hammer home how most would benefit from lower taxes.

But even if Republicans can keep voters focused on tax cuts, Van Hollen said Democrats have other reasons to be optimistic.

"If anyone would have predicted ... we'd be in this strong of a position as we are today a year ago ā€” I don't think they would have predicted this," he said. "That said, we've got a big fight ahead."

"The good news is we've got a lot of energy and momentum in support of Democrats," Van Hollen said, pointing to the result in the Alabama Senate contest where Sen. Doug Jones, D-Ala., defeated Judge Roy Moore.

Republicans hold a slim 51-49 majority in the Senate. Republicans also hold an advantage in the 2018 map with only eight of their members up for re-election compared to 24 Democrats. But Democrats only need to pick up two seats to win the majority, and they've targeted seats in Arizona and Nevada.

In Arizona, both Rep. Martha McSally and former Maricopa County Sheriff Joe Arpaio announced their campaigns on the GOP side. While McSally's announcement was expected after a two-month whisper campaign, Arpaio's was not, and he could shake up the race that also includes former Republican state Sen. Kelli Ward in what could be the most contentious GOP primary of the year.

Meanwhile, House Democrats are feeling the wind at their back after a string of retirements from the House Republican ranks, including four more since the beginning of the new year: Reps. Darrell Issa of California; Ed Royce of California, the chairman of the House Foreign Affairs Committee; Gregg Harper of Mississippi, chairman of the House Administration Committee; and McSally.

Twenty-one House Republicans are not seeking re-election to the House, and Democrats believe some of these seats give them a chance to win back the 25 needed to retake the majority.

"This is a year like none other," House Minority Leader Nancy Pelosi, D-Calif., said during her weekly press conference on Thursday. "Last year and this [year], we've seen overwhelming enthusiasm. People following the election in 2016 saw the urgency, wanted to take responsibility, and that gives us opportunity."