Many investors are withdrawing their money from the stock market right now, but those focused on the long term know to hold on through market volatility. In fact, it's still a great time to invest in companies that have excellent underlying businesses and attractive long-term prospects. Dividend payers that have maintained a reliable payout program for a while fit the bill.

With that, let's consider two dividend-paying companies that look like strong buys for the next two decades: Medtronic (MDT -0.19%) and Merck (MRK 3.72%).

1. Medtronic

Medtronic, a leader in medical devices, could feel the impact of President Trump's tariffs. The company markets hundreds of devices across dozens of countries, but generates much of its revenue from the U.S. and does a significant amount of manufacturing abroad, including in Mexico and China, the latter of which has been a favorite target of the current administration's tariffs.

So, Medtronic's near-term prospects seem somewhat uncertain, but it remains a solid long-term investment. One reason is that Medtronic has been around for a while and has navigated challenging economic and market conditions before. While past success doesn't guarantee anything, it at least tells us quite a bit about a company and its underlying business. Medtronic is a highly successful company that has the financial flexibility to mitigate the impact of tariffs, at least to some extent, perhaps by strengthening its U.S.-based manufacturing footprint.

Medtronic is already considering ways to do that. Further, thanks to its operating in a defensive industry, Medtronic's business will fare better than most in bad times. The company markets devices across several therapeutic areas, ranging from options for diabetics to surgical solutions. Patients with diabetes are unlikely to forgo buying an insulin pump even in a recession; they will seek to cut other expenses first. Medtronic's financial results should remain pretty steady, as they have for a long time.

MDT Revenue (Annual) data by YCharts

The company rarely blows the market out of the water with incredible revenue or earnings growth, but its consistency over long periods is impressive. Medtronic also has significant growth opportunities, including in diabetes care and through its robotic-assisted surgery device, the Hugo system, which is currently being tested in the U.S. Lastly, Medtronic has an impressive dividend track record. The company has increased its payouts for 47 consecutive years. Medtronic's forward yield of 3.4% also looks competitive.

Like many healthcare leaders, the stock has outperformed the market this year. Medtronic could do the same for investors patient enough to hold its shares for the next two decades.

2. Merck

Merck hasn't performed well in the past year as potential competition for its biggest cash cow, cancer drug Keytruda, seems to be mounting. The challenges to Keytruda also include an upcoming patent cliff -- arguably the second-biggest this decade, after AbbVie's Humira. These issues are real and could lead to Merck not keeping pace with the market in the near to mid-term. However, the company's long-term prospects are still strong. Pharmaceutical giants often go through tough periods after major patent expirations.

The key to recovery from these is developing newer and better medicines. Or, occasionally, newer versions of older drugs. That's what Merck is doing. It is working on a subcutaneous formulation of Keytruda that should generate strong sales well into the 2030s. But it has other tricks up its sleeves. Merck's newer approvals include medicines such as Winrevair, a therapy for pulmonary arterial hypertension. The company has a deep pipeline with several dozen other programs in development.

It is still seeking more. Merck has signed licensing agreements with smaller companies lately to enter the fast-growing weight loss market and the emerging field of bispecific antibodies, a relatively new class of therapies that could help develop more effective treatments, especially in oncology. Merck is also one of the largest animal health companies in the world, which could help drive solid long-term results, especially as pet ownership continues to rise.

The drugmaker's greatest strength isn't Keytruda. It is its innovative qualities that have allowed it to generate excellent returns over many decades. Merck has maintained a solid dividend program for a long time, too. Over the past 10 years, it has increased its payouts by 80%; it currently offers a forward yield of 3.4%. Despite recent issues, Merck is worth investing in for the long haul, especially for income-seeking investors.